JPH04318404A - Fine and coarse adjustment interlocking type scanning tunnel microscope - Google Patents

Abstract

PURPOSE:To enable a probe to trace the surface of a sample even when the surface is greatly rough by interlockingly moving a fine adjustment mechanism and a coarse adjustment mechanism based on the minute displacement state of the probe in an approaching/separating direction to the sample. CONSTITUTION:A tunnel current detector 6 detects a tunnel current which starts to flow when a probe 1 approaches the surface of a sample 2 with the distance of the atomic level, with feeding the current as a signal to a fine adjustment mechanism control device 7. An instruction signal to control the fine adjustment of the probe 1 is supplied from the device 7 to a fine adjustment mechanism 3. A device 10 for detecting/evaluating the state of the fine adjustment mechanism receives positional data in the Z-axis direction of the probe 1 input from the device 7, compares with a reference data, and activates a coarse adjustment mechanism control device 9 when it judges that the position of the probe 1 cannot be changed as required only by the shift through the fine adjustment. When a coarse adjustment mechanism 4 is to be driven, the device 9 supplies arm instruction signal, upon necessities, to the device 7 so as to execute a required adjustment to the position of the probe 1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a scanning tunneling microscope with coarse and fine movement, and in particular, a coarse movement mechanism and a fine movement mechanism that adjust the distance of a probe to a sample are linked to eliminate unevenness on the surface of the sample. This article relates to a scanning tunneling microscope with coarse and fine movements that enables measurement even in large cases.

0002

[Prior Art] In measurement operations using a scanning tunneling microscope, a probe is brought close to the surface of a sample to be observed at an atomic level distance, and a tunneling current is passed between the probe and the sample surface. In this state, when the probe is scanned over the surface of the sample for measurement, the distance of the probe relative to the sample surface is kept constant so that the tunneling current value is always constant. In such measurement operations, when the probe scans the surface of the sample, it follows the unevenness of the sample surface and changes its position in a state of slight movement. Data regarding the unevenness of the image can be obtained as image information. In order to cause a tunnel current to flow when a predetermined distance is reached between the probe and the sample surface, it is necessary to apply a required voltage to the probe from a voltage source. Further, the tunneling current taken out from the probe is constantly observed, and servo control is performed on the position of the probe based on changes in the value of the obtained tunneling current. In the signal processing system, data on the surface scanning of the probe and data on the distance between the probe and the sample surface are stored, and these data are used to create image information of the sample surface. To adjust the distance between the probe and the sample surface, a coarse movement mechanism that changes the position of the probe over large distances and a fine movement mechanism that changes the position of the probe over small distances are used. The probe is attached, for example, to a predetermined location of a fine movement mechanism called a tripod, which consists of three fine movement piezoelectric elements arranged at right angles.
Further, this fine movement mechanism is disposed in a coarse movement mechanism that moves the probe only in the direction of approaching and moving away from the sample. In this way, the position of the probe is adjusted by the coarse movement mechanism and the fine movement mechanism. The coarse movement mechanism normally operates only to move the probe to a distance that allows tunneling current to flow, while the fine movement mechanism moves the probe close to the sample surface and moves the probe to the distance between the probe and the sample surface. It operates to adjust the distance so that the tunnel current becomes a constant current. Therefore, since the operations of the coarse adjustment mechanism and the operations of the fine adjustment mechanism have different purposes,
It was common for each operation to be performed under independent control.

[0003]Also, while the coarse movement mechanism is operating, the fine movement mechanism is servo controlled. Although these operations appear to be linked, it is difficult to understand the operating status of both mechanisms. Since they were not operating, the control operations were not substantially linked.

0004

[Problems to be Solved by the Invention] In conventional scanning tunneling microscopes, each operation of the coarse movement mechanism and fine movement mechanism is independent, and each movement is not configured to interlock with each other. When the fine movement mechanism reaches its limit due to large irregularities on the sample surface while measuring a predetermined area on the sample surface,
Problems arose in which measurements became impossible, or the probe could no longer escape, causing the probe and sample to collide and damage both. Collisions due to the inability to follow the unevenness of the sample surface as described above occur frequently when the unevenness is large, and each time the scanning tunneling microscope must be stopped and the measurement operation performed again, the measurement operation This has the disadvantage that it becomes extremely troublesome.

[0005] In view of the above problems, an object of the present invention is to control the coarse movement mechanism and fine movement mechanism so that their operations are interlocked, so that even when the surface of a sample has large irregularities, it is possible to follow the surface. The object of the present invention is to provide a scanning tunneling microscope that combines dynamic and fine movements.

[0006]

[Means for Solving the Problems] A scanning tunneling microscope coupled with coarse and fine movements according to the present invention includes a probe, a coarse movement mechanism that greatly changes the position of the probe with respect to the surface of the sample, and a coarse movement mechanism that greatly changes the position of the probe with respect to the surface of the sample. a fine movement mechanism that changes the position of the probe small at the top, a voltage application means that applies a voltage to cause a tunnel current to flow between the probe and the sample, a measurement means that measures the tunnel current, and a tunnel to be measured. A fine movement mechanism control means that controls the distance between the probe and the sample via the fine movement mechanism so that the current value is held constant, and scans the surface of the sample with the probe via the fine movement mechanism; A scanning tunneling microscope equipped with a data processing means for recording and processing data regarding the surface of a sample obtained with a needle, and a display means for displaying the surface of the sample as an image, the coarse movement mechanism controlling the operation of the coarse movement mechanism. The control means and the position of the probe driven by the fine movement mechanism are detected within the movable range of the fine movement mechanism, and based on this detection information, a command is given to the coarse movement mechanism control means, and the probe is driven by the fine movement mechanism. The probe is configured to include a fine movement mechanism state detection/judgment means for displacing the position of the probe so that it is within the movable range. In the above configuration, the coarse movement mechanism control means issues a command to the fine movement mechanism control means when receiving a command signal from the fine movement mechanism state detection/judgment means, and positions the probe at an appropriate position within the movable range by the fine movement mechanism. As described above, the probe is characterized in that the probe is finely displaced depending on the coarse displacement. In the above configuration, the fine movement mechanism state detection/judgment means is characterized in that the fine movement mechanism state detection/judgment means obtains position information due to fine movement of the probe from the fine movement mechanism control device or the fine movement mechanism.

[0007]

[Function] In the scanning tunneling microscope with coarse and fine movements linked according to the present invention, the displacement of the probe in the direction toward and away from the sample is monitored by the fine movement mechanism and the fine movement mechanism. The movement mechanism is configured to be able to interlock,
When the sample surface has large irregularities and needs to be moved outside the fine movement range, the coarse movement mechanism control means and the coarse movement mechanism are operated based on commands from the fine movement mechanism state detection/judgment means;
moving the probe out of the movable range by coarse movement and simultaneously operating the fine movement mechanism control means and the fine movement mechanism;
Adjust the movement position by the fine movement mechanism to the required position. The above series of operations are performed automatically.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing the system configuration of a scanning tunneling microscope according to the present invention, and FIG. 2 is a perspective view showing the movement relationship of a probe with respect to a sample. In FIG. 1, 1 is a probe, and 2 is a sample. The probe 1 is the sample 2
In contrast, the tip portion is arranged so as to face the measurement surface of the sample 2 at an angle substantially perpendicular to the measurement surface. The probe 1 is usually made of a conductive material so that tunneling current flows therethrough. In the illustrated example, the probe 1 is placed horizontally and the sample 2 is placed vertically, but the orientation of these can be arbitrarily selected. Probe 1
is attached to the fine movement mechanism 3. The structure of the fine movement mechanism 3 is
For example, since it is known as a tripod fine movement element, it is not shown in detail. To give an overview of the tripod fine movement element, it is equipped with three piezoelectric elements in the axial direction of the probe 1 (referred to as the Z-axis direction) and in the X-axis and Y-axis directions perpendicular to this. The distance between the probe 1 and the sample 2 is adjusted, that is, the probe 1 is moved toward and away from the sample (or moved forward and backward), and the measurement surface of the sample is scanned with the piezoelectric element in each direction of the X and Y axes. It is composed of The directions of each axis are shown in FIG. The piezoelectric elements involved in the displacement of the fine movement mechanism 2 in each axial direction are piezoelectric elements for fine movement that cause the probe 1 to be displaced by several μm to more than ten μm. This fine movement mechanism 2 further includes a coarse movement mechanism 4.
attached to the front end of the The coarse movement mechanism 4 is commonly called an inchworm, and has a function of moving the probe 1 over a large distance relative to the sample 2. To outline the structure of the coarse movement mechanism, it consists of a coarse movement piezoelectric element that expands and contracts, and front and rear clamp parts disposed before and after the coarse movement piezoelectric element for clamping or unclamping the coarse movement piezoelectric element. In the coarse movement mechanism 4, by operating the piezoelectric element and the front and rear clamp parts at appropriate timings, a scooping movement is performed, the probe 1 is coarsely moved, and the distance between the probe 1 and the sample 2 is reduced. change. On the other hand, the sample 2 is fixed to a sample stage 5. In fact, other components for supporting the coarse movement mechanism 4 and the sample stage 5 are provided around it. but,
A detailed explanation will be omitted here.

A tunnel current detector 6 is disposed between the probe 1 and the sample 2. The tunnel current detector 6 includes a power supply element for causing a tunnel current to flow therein, and applies a relatively low predetermined voltage between the probe 1 and the sample 2. In this state, when the probe 1 approaches the surface of the sample 2 at an atomic level distance, a tunnel current flows, and this tunnel current is detected and given as a signal to the next-stage fine movement mechanism control device 7. The fine movement mechanism control device 7 has, as a first function, a function of giving a command signal for controlling the fine movement of the probe 1 to the fine movement mechanism 3, thereby controlling the fine movement of the probe 1 for measurement. . As described above, the fine movement mechanism 3 has three piezoelectric elements for fine movement in each axial direction, and each piezoelectric element for fine movement is basically independently controlled by the fine movement mechanism control device 7. In the piezoelectric element for fine movement in the Z-axis direction, the distance of the probe 1 to the sample surface is kept constant by a servo circuit (not shown) in the fine movement mechanism control device 7 so that the detected tunnel current is always a constant value. Servo control is performed. In addition, the piezoelectric elements for fine movement in each direction of the X-axis and Y-axis are controlled by an XY scanning section (not shown) in the fine movement mechanism control device 7 to scan the area where measurement is required. . In addition, the fine movement mechanism control device 4
is further equipped with a signal processing device (not shown) inside, and its second function is to use the position data of the probe 1 in the X, Y, and Z axis directions determined by the signal processing device. It has a function of displaying an image regarding the measurement surface of the sample 2 on the data display device 8.

Next, 9 is a coarse movement mechanism control device. This coarse movement mechanism control device 9 controls the probe 1 by the above-mentioned coarse movement mechanism 4.
This is a means for controlling approach and departure movements due to coarse movement. The coarse movement mechanism control device 9 controls the expansion and contraction operations of the coarse movement piezoelectric element and the clamping and unclamping operations of the front and rear clamp sections at appropriate timings, and causes the coarse movement mechanism 4 to perform a scoop-like movement. , causes the probe 1 to perform coarse movement. Since this configuration and operation are known, detailed explanation will be omitted.

Referring to FIG. 2, the positional relationship between the probe 1 and the measurement surface of the sample 2 and the direction of movement of the probe 1 can be clearly understood.

Next, a fine movement mechanism state detection/determination device 10 is further provided between the fine movement mechanism control device 7 and the coarse movement mechanism control device 9. The fine movement mechanism state detection/judgment device 10 inputs the position data of the probe 1 in the Z-axis direction from the fine movement mechanism control device 7, and uses this position data as a standard regarding the operational performance of the piezoelectric element in the Z-axis direction of the fine movement mechanism 3. It has a function of operating the coarse movement mechanism control device 9 when comparing the data and determining that the required positional change cannot be given to the probe 1 only by the displacement by the fine movement piezoelectric element. Further, when operating the coarse movement mechanism 4 based on the operation command from the fine movement mechanism state detection/judgment device 10, the coarse movement mechanism control device 9 sends information regarding the position of the probe 1 to the fine movement mechanism control device 7 as needed. It is configured to provide command signals for making the required position adjustments. Fine movement mechanism control device 7 accompanying the detection operation of the fine movement mechanism state detection/judgment device 10
A specific example of each control operation of the coarse movement mechanism control device 9 will be explained. The fine movement mechanism state detection/judgment device 10 detects the probe 1 based on each operation of the fine movement mechanism control device 7 and the fine movement mechanism 3.
When the following conditions (1) to (3) occur while the probe is scanning by following the irregularities on the predetermined surface of the sample 2, the coarse movement mechanism control device 9 is operated and the probe 1 is The position in the Z-axis direction is controlled by a composite operation of the respective operations of the fine movement mechanism 3 and the coarse movement mechanism 4.

(1) When the piezoelectric element in the Z-axis direction of the fine movement mechanism 3 reaches the limit of its movable range (or an arbitrarily set threshold distance) due to the separation operation, the coarse movement mechanism control device Through the control operation 9, the coarse movement mechanism 4 is caused to perform a movement operation in the separating direction. The amount of movement by the coarse movement mechanism 4 is, for example, 1/2 of the movable range of the piezoelectric element by the fine movement mechanism 3. At the same time, the coarse movement mechanism control device 9 issues a command to the fine movement mechanism control device 7 to perform control to displace the position of the probe 1 by the fine movement mechanism 3 to the center position of the movable range by the fine movement mechanism 3. . As a result, the coarse movement mechanism 4
After the predetermined amount of movement by the fine movement mechanism 3, the fine movement of the probe 1 can be continued near the center of the movable range by the fine movement mechanism 3. (2) When the piezoelectric element in the Z-axis direction of the fine movement mechanism 3 reaches the limit of its movable range (or an arbitrarily set threshold distance) during the approach operation, the control of the coarse movement mechanism control device 9 Through the operation, the coarse movement mechanism 4 is caused to perform a movement operation in the approaching direction. The amount of movement by the coarse movement mechanism 4 is, for example, 1/2 of the movable range of the piezoelectric element by the fine movement mechanism 3. In this case, the coarse movement mechanism control device 9 instructs the fine movement mechanism control device 7 to adjust the position of the probe 1 driven by the fine movement mechanism 3 to the end of the movable range of the fine movement mechanism in the direction of separation. A command is issued to control the displacement. After a predetermined amount of movement by the coarse movement mechanism 4, the fine movement mechanism control device 7
The probe 1 is moved closer to the position until the tunneling current is detected again, and the fine movement for measurement is continued. (3) If the movement of the probe 1 by the fine movement mechanism 3 oscillates between the limits of the approach direction and the separation direction in the movable range and is not stable, the coarse movement mechanism control device 9 causes the coarse movement mechanism 4 to move the probe 1. The probe 1 is moved largely in the direction of separation so as not to reach the limit of the range in the direction of approach. This situation is a case where the situations (1) and (2) described above occur almost simultaneously. In this situation, the probe 1 is
This occurs when the distance between the sample 2 and the sample 2 changes, or when trying to measure a sample 2 with a highly uneven surface at a speed higher than the response speed of the control system.

In determining each of the conditions (1) to (3) above, the fine movement mechanism state detection/judgment device 10
is internally equipped with arithmetic processing means and determination means. Then, by these means, position data between the probe 1 and the surface of the sample 2 is captured, and compared with data indicating the limit of the movable range of the piezoelectric element in the Z-axis direction of the fine movement mechanism 3, etc., and the required conditions are determined. When the conditions are satisfied, a command for executing each of the above-mentioned controls is output to the coarse movement mechanism control device 9.

In the embodiment described above, the fine movement mechanism state detection/judgment device 10 obtained the position data of the probe 1 from the fine movement mechanism control device 7, but it is configured to obtain the position data directly from the fine movement mechanism 2. You can also.

[0016]

As is clear from the above description, according to the present invention, the movement of the probe is configured such that the movement operation by the fine movement mechanism and the movement movement by the coarse movement mechanism can be linked under predetermined conditions. If the fine movement mechanism reaches the limit of its movable range in the approach and departure directions during measurement of the sample surface, the coarse movement mechanism can be activated to substantially expand the movable range and prevent the probe from colliding with the sample. can be prevented and its damage can be prevented. Moreover, since such interlocking operations can be performed automatically, there is no need for special monitoring by the operator. Furthermore, with conventional scanning tunneling microscopes, when the sample surface has large irregularities, collisions occur frequently and the measurement cannot be completed in one operation, but with the scanning tunneling microscope of the present invention, collisions can be reliably avoided. This makes it possible to complete the measurement in one measurement operation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a scanning tunneling microscope according to the present invention.

FIG. 2 is a perspective view of essential parts for illustrating the movement relationship between the probe and the surface of the sample.

[Explanation of symbols]

1 Probe 2 Sample 3 Fine movement mechanism 4 Coarse movement mechanism 5　　　　　　　　　Sample stage

Claims (4)

[Claims] 1. A probe, a coarse movement mechanism that greatly changes the position of the probe with respect to the surface of the sample, and a fine movement mechanism that small changes the position of the probe on the surface of the sample.
voltage applying means for applying a voltage for causing a tunnel current to flow between the probe and the sample; a measuring means for measuring the tunnel current; fine movement mechanism control means for controlling the distance between the probe and the sample via a fine movement mechanism and causing the probe to scan the surface of the sample via the fine movement mechanism; A scanning tunneling microscope comprising a data processing means for recording and processing data regarding the surface of the sample, and a display means for displaying the surface of the sample as an image, a coarse movement mechanism control means for controlling the operation of the coarse movement mechanism; , the position of the probe driven by the fine movement mechanism is detected within the movable range of the fine movement mechanism, and based on this detection information, a command is given to the coarse movement mechanism control means, so that the probe is A scanning tunneling microscope coupled with coarse and fine movements, comprising fine movement mechanism state detection/judgment means for displacing the position of the probe so that it is within a movable range of the fine movement mechanism. 2. The coarse movement/fine movement interlocking type scanning tunneling microscope according to claim 1, wherein the coarse movement mechanism control means comprises:
When a command signal is received from the fine movement mechanism state detection/judgment means, a command is issued to the fine movement mechanism control means to adjust the displacement due to coarse movement so that the probe is at an appropriate position within the movable range of the fine movement mechanism. A coarse/fine movement interlocking type scanning tunneling microscope characterized in that the probe is finely displaced depending on the movement of the probe. 3. In the scanning tunneling microscope coupled with coarse and fine movement according to claim 1, the fine movement mechanism state detection/judgment means detects position information due to fine movement of the probe.
A coarse movement characterized by being obtained from the fine movement mechanism control device.
Micro-motion-linked scanning tunneling microscope. 4. In the scanning tunneling microscope coupled with coarse and fine movement according to claim 1, the fine movement mechanism state detection/judgment means detects position information due to fine movement of the probe.
A scanning tunneling microscope with coarse and fine movements coupled to the fine movement mechanism.