JPH0413901A - Scanning-type tunnel microscope with function of discriminating shape of fore end of probe and discriminating method thereof - Google Patents

Abstract

PURPOSE:To discriminate the appropriateness of the shape of the fore end of a probe by adding a scanning direction control device and an image display control device to a scanning-type tunnel microscope and by preparing and displaying an image by scanning the probe in different directions in respect to the same sphere of the surface of a sample. CONSTITUTION:A scanning-type tunnel microscope comprises a probe 101, a scanning device 104, a scanning control device 105, a signal processing device 103, an image storage device 106 and an image display device 107 and observes a sample 102. In order to discriminate the shape of the fore end of the probe 101, a scanning direction control device 1 and a screen control device 2 are provided. By the scanning direction control device 1, scanning is made in normal and reverse directions, oppositely, at least in one direction in the same sphere of the surface of the sample 102. The image display control device 2 prepares an image corresponding to each of the above- mentioned normal and reverse scanning and displays images thus prepared in the image display device 107. The displayed images in a plurality are compared and thereby the appropriateness of the shape of the fore end of the probe is discriminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a scanning tunneling microscope with a probe tip shape identification function and a probe tip shape identification method, and in particular, the present invention relates to a scanning tunneling microscope with a probe tip shape identification function and a probe tip shape identification method. The present invention relates to a scanning tunneling microscope with a probe tip shape identification function and a probe tip shape identification method that can check whether the shape is suitable or not.

[Conventional technology]

A scanning tunneling microscope will be explained. - Figure 12 shows the configuration of a scanning tunneling microscope known for boat fishing. In FIG. 12, 101 is a probe for generating tunnel current;
]-02 is a sample to be measured; 103 is a signal processing device that applies a voltage between the probe 101 and the sample 1-02 and detects a tunnel current;
1.05 is a scanning device 104 that scans the sample surface by making slight movements in the x, y, and z directions that form the dimensions;
An image storage device 106 receives signals from the signal processing device 103 and the scan control device 105, converts the signals into pixel signals, and stores the pixel signals.
7 is an image display device that displays pixel signals provided from the image storage device 106 on a screen.

In the above configuration, the signal processing device 103
01 and sample”. When a voltage is applied between the probe 101 and the sample 02 and the probe 101 and the sample 02 are brought close to each other on the order of angstroms, non-contact occurs between the atoms located at the tip of the probe 1.01 and the atoms on the surface of the sample 102. A tunnel current flows under the condition. This tunnel current is a current that flows based on the tunnel effect due to quantum mechanics. The current value of this tunnel current has a characteristic that it responds extremely sensitively to changes in the distance between the probe 101 and the sample 102. Therefore, the tunneling current is detected by the signal processing device 103, and the position of the probe 101 is controlled by the scanning device 104 so that the distance between the probe 101 and the sample 102 is constant in order to keep the current value of the tunneling current constant. At the same time, the axial direction of the probe 101 (
The surface of the sample 102 is scanned by scanning in a plane (defined as an XY plane) perpendicular to the two directions (defined as two directions). The resulting signal regarding the amount of movement of the probe 101 in the Z direction is converted into a pixel signal, and is sent to and stored in the image storage device 106 as pixel data on the image formed by the X and Y coordinates of the scanning device 104. . By outputting this pixel data to the image display device 107, the surface shape of the sample 102 can be measured with an accuracy of interatomic distance. Note that it is also possible to configure the scanning in two directions to be constant without performing scanning, and to use changes in the magnitude of the tunnel current as a pixel signal.

Prior art related to the above-mentioned scanning tunneling microscope includes Japanese Patent Application Laid-Open No. 63-26936 and Japanese Patent Application Laid-Open No. 61-2.
33304, Japanese Unexamined Patent Publication No. 63236904, and the like.

[Problem to be solved by the invention]

In a scanning tunneling microscope, a high-resolution image cannot be obtained unless a tunneling current is always generated from a specific single atom at the tip of the probe 1-01 during scanning in the X and Y directions. Therefore, the tip of the probe 1-01 needs to have a sharp shape that makes it easy to identify a single atom, and it is extremely important that the tip is sharp. However, it is extremely difficult to check whether the tip shape of a probe actually made is sharp or not, and even when examined using a scanning electron microscope, it is difficult to recognize the shape. It was time-consuming. As a result, in the past, it was not possible to adequately select the quality of the probe 101 after it was manufactured, and depending on the shape of the tip of the probe, the image may become unclear or
There was a problem in that the sharpness of the image differed depending on the way the probe was attached.

Therefore, when performing measurements using a scanning tunneling microscope, users prepare multiple probes 1-01, replace them at appropriate timings, and create images many times until the final image becomes one. A problem occurred in that it was necessary to obtain the clearest image possible.

An object of the present invention is to provide a probe tip shape identification function that can easily check whether the tip shape of the probe is sharp or not by using the function itself of the scanning tunneling microscope to which the probe is attached. An object of the present invention is to provide a scanning tunneling microscope and a probe tip shape identification method.

[Means to solve the problem]

A scanning tunneling microscope with a probe tip shape identification function according to the present invention includes a probe disposed close to a sample, and a signal processing means for applying a voltage between the probe and the sample to detect a tunneling current. a scanning means for changing the position of the probe to scan the sample surface; a scanning control means for controlling the scanning of the sample surface by the probe via the scanning means; and a scanning means for controlling the scanning of the sample surface by the probe. image storage means for taking in data to create and store an image signal based on this data; and image display means for displaying an image of the sample surface scanned by the probe based on the image signal created by the image storage means. In a scanning tunneling microscope, a scanning direction control means for scanning a specific range of a surface of a sample in at least one direction in forward and reverse directions, and creating images corresponding to each of the forward and reverse scans; The probe includes an image display control means for separately displaying the images on the image display device, and is configured to identify the shape of the tip of the probe by comparing the plurality of images displayed on the image display device.

In the scanning tunneling microscope with a probe tip shape identification function according to the present invention, in the device configuration described above, at least one direction can be one of the orthogonal X direction and Y direction.

In the scanning tunneling microscope with a probe tip shape identification function according to the present invention, in the above-described device configuration, the image display device is
It is characterized by simultaneously displaying four images obtained by scanning in each of the X positive direction, the X negative direction, the Y positive direction, and the Y negative direction.

The probe tip shape identification method for a scanning tunneling microscope according to the present invention scans a probe in two opposite scanning directions in at least one direction over a specific range on the surface of a sample. The method is characterized in that the tip shape of the probe is identified by creating at least two images of the same range, displaying these images on at least one image display device, and comparing the displayed plurality of images. do.

[Effect]

In the scanning tunneling microscope with a probe tip shape identification function according to the present invention, a specific range is set on the surface of the sample, and at least two scanning directions having opposite directions are set for this range by a scanning direction control device, The probe is scanned according to the normal measurement function according to these scanning directions, and based on the scanning data, an image storage device and an image display control device are used to create at least two images of the same area but in opposite scanning directions, and these images are Images are displayed on an image display device for comparison.

In the probe tip shape identification of a scanning tunneling microscope according to the present invention, at least two images are created in different scanning directions for the same specific area on the sample surface, so that the tip of the probe is not completely sharp. If not, there will be a difference between at least two images, and this will allow the shape of the tip of the probe to be identified and evaluated.

〔Example〕

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

The hardware configuration of the scanning tunneling microscope with probe tip shape identification function according to the present invention is basically the same as the configuration shown in FIG. 12. FIG. 1 shows the configuration of an apparatus according to the present invention, and the same elements as in FIG. 12 are given the same reference numerals. FIG. 2 shows an enlarged view of the image display device and is a diagram for explaining an image display method, and FIG. 3 is a flowchart showing an example of a scanning and image display procedure.

The operation will be outlined based on FIG. A probe 101 is attached to a scanning device 1.4, and the scanning device 104 is controlled by a scanning control device 105. A potential difference is applied between the probe 101 and the sample 102 by the signal processing device 1-03, and as a result, a tunnel current flowing between the probe 101 and the sample 1-02 is detected by the signal processing device 103. The detected tunnel current is sent to the scan control device 105,
For example, the scanning control device 105 controls the operation of the scanning device 104 so that the magnitude of the tunnel current is constant. Data regarding the amount of scanning performed so that the tunnel current is constant is sent from the scan control device]-05 to the image storage device 106, where it is converted into a pixel signal and sent to the image display device 10.
7 is displayed. Furthermore, if the magnitude of the tunnel current is not controlled to be constant, data regarding the current value of the tunnel current is sent from the signal processing device 103 to the image storage device 106, and here the magnitude of the tunnel current is converted into a pixel signal. The image is converted and displayed on the image display device 107.

By repeating the above operations on the surface of the sample 102, a surface image of the sample 102 can be obtained on the screen of the image display device 107.

In the scanning tunneling microscope according to the present invention, a scanning direction control device 1 and an image display control device 2 are further added to the above configuration. The scanning direction control device 1 gives a predetermined command to the scanning control device 105 when executing the probe tip shape identification function,
It has a function of moving the probe 101 in forward and reverse scanning directions in two directions, for example, orthogonal X and Y directions, in an arbitrarily set specific range on the surface of the sample 102. The image display control device 2 also has the function of giving a predetermined command to the image storage device 1.06 when executing the probe tip shape identification function, and displaying, for example, four split screens in the way the image is displayed on the image display device 107. has. In FIG. 1, the scanning direction control device 1 and the image display control device 2 are shown as separate means for convenience of explanation, but
It is also possible to integrate the two functional means described above.

As shown in FIG. 2, the image display device 107 displays four images simultaneously on one screen. Here, a measurement range is set in an arbitrary area on the surface of the sample 102. In Fig. 2, the upper left is image 3 created by repeatedly scanning the probe 101 only in the positive X direction, and the upper right is the image 3 created by repeatedly scanning the probe 101 only in the
Image 4 is created by repeatedly scanning n times only in the negative direction of This is an image 6 created by repeatedly scanning the probe 101 only in the positive X direction n times. Images 3 to 6 above all show images of the same area on the sample surface. In each image, a line indicated by an arrow indicates the direction of scanning movement of the probe 101,
This movement is performed by the scanning device 104 receiving a command from the scanning direction control device 1 via the scanning control device 105.

Operation control in the scanning tunneling microscope for displaying the image shown in FIG. 2 on the image display device 107 will be explained based on FIG. 3.

First, when a command to identify the tip shape of the probe is given and a control operation is started, the probe "01" is slightly moved by the scanning device 104 to perform the first (YO) scan in the X positive direction (step 11), whereby the scanning control device 10
The scan data obtained in step 5 is given to the image storage device 106, and the image data obtained here is displayed on image 3 on the image display device 107 (step 12). Said step 11
A command for executing is given from the scanning direction control device 1 to the scanning device 104 via the scanning control device 105. Further, a command for executing step 12 is given from the image display control device 2 to the image storage device 1-06 having a normal image data creation and storage function. This point also applies to the following operations.

Next, scanning is performed in the negative X direction (step 13), and image data is displayed on the image 4 based on the scanning data obtained in this scanning (step 14). The scans performed in steps 1-1 and 13 are in a relationship such that the same location is scanned from opposite sides. Therefore, the images displayed in images 3 and 4 represent the same area.

In the next judgment step 15, it is judged whether or not Yi is equal to Yn. If not, the process moves to the next scanning line and steps 11-14 are repeated (step 16).

When images 3 and 4 are completed, Yi becomes Yn, so the process moves to step 17 through decision step 15. In steps 17 to 20, regarding the creation of images 5 and 6, scanning is performed in the same way in the positive and negative directions of the Y axis, and in step 2
1 and 22, scanning in the Y direction is repeated n times, resulting in images 5 and 6.
is completed.

In this way, four images 3 to 6 are created and displayed on one screen of the image display device 107. These four screens showing the same area on the surface of the sample 102 can be used to determine whether the tip shape of the probe 101 is appropriate. The person making the identification decision is the person scanning the scanning tunneling microscope, and the decision is made by comparing the four screens.

Next, a method for identifying the tip shape of the probe 101 based on images 3 to 6 will be described.

The types of tip shapes of the probe 101 will be explained based on FIGS. 4 to 7. FIG. 4 shows the ideal tip shape. If this is enlarged, it will look like FIG. 8.

In FIG. 8, 102a is the surface of the sample 102,
31 indicates the arrangement of atoms, 101a indicates the tip of the probe 101, and 32 indicates the arrangement of atoms at the tip.

According to the shape of this probe tip, the surface 10 of the sample 102
The single atom closest to the tip of the probe 2a is identified, and since the tunneling current 33 is generated only in one atom at the tip of the probe 102, a stable image can be obtained. In other words, the probe 10 having such a tip shape
Among images 3 to 6 created in step 1, the same clear image can be obtained in all images.

Most of the tips of the probes actually manufactured have shapes as shown in FIGS. 5 and 6. The tip shape shown in Fig. 5 has a deformed tip, but
Since there are sharp parts and specific atoms involved in the flow of tunneling current, a clear image can be obtained as in the example of FIG. 4.

In the shape of the tip of the probe shown in FIG. 6, there is no sharp portion. When this is enlarged, it becomes as shown in Fig. 9. With this probe, it is not possible to identify one atom in the atomic array 32 at the tip of the probe 101 to the surface 102a of the sample 102, and a tunnel current is generated from any one of the multiple atoms. 33 occurs. For this reason, the probe 101
Even if the image is scanned, a stable signal cannot be obtained and the image becomes unclear. Therefore, all of the above-mentioned images 3 to 6 become unclear. The tip shape shown in FIG. 7 includes a mixture of sharp parts and rounded parts. When an image is created using the probe 101 having such a tip shape, the sharpness of the image varies depending on the deflection of the probe due to the scanning direction of the probe 101 and the like. An example of this will be explained based on FIGS. 10 and 11.

FIG. 10 shows the case where the probe 101 is scanned in the right direction A in the figure. In this case, since the sharp portion 34 is closer to the surface 102a of the sample than the rounded portion 35, the tunnel current 33 flows in the sharp portion 34, making it impossible to obtain a clear image as in the example shown in FIG. can. On the other hand, FIG. 11 shows the case where the probe 101 is scanned in the left direction B in the figure.

In this case, since the rounded portion 35 is closer to the sample surface 102a than the sharp portion 34, the tunnel current 33 flows in the rounded portion 35, and the image created becomes unclear, similar to the example described in FIG. 9. Therefore, when scanning is performed using a probe having the tip shape shown in FIG. 7, there is a characteristic that the sharpness of the image, the pattern, etc. change when the scanning direction is changed.

As is clear from the above description, the shape of the tip of the probe 101 can be identified by visually recognizing the four images 3 to 6 scanned in different scanning directions.

Specifically, when images 3 to 6 are all clear images, a probe with a good tip shape as shown in Fig. 5, and images 3 to 6 are used.
6 are all unclear images, the probe with the defective tip shape shown in FIG. 6, the image in the scanning direction consisting of images 3 to 6 is clear, and the remaining images in the scanning direction are unclear. In some cases, it can be identified as a defective probe having the tip shape shown in FIG.

In the above embodiment, scanning is performed in the forward and reverse scanning directions in each of the X direction and the Y direction to create four images for comparison, but for example, if the scanning direction is different in only one direction, It is also possible to create two images and compare them. For comparison,
It is sufficient to have at least two types of images. Furthermore, as shown in FIG. 1, by providing the determination device 40 in the image storage device 106, the image signals themselves are compared without being displayed as images on the image display device 107, and a computer or the like automatically determines whether the probe is good or not. It can also be configured to determine. In this case, since there is no need to create an image, one scan in each scanning direction is sufficient. Therefore, the measurement time for identifying the tip shape of the probe can be shortened. Furthermore, the image display device 107 can be configured to display a plurality of images by switching them on one screen.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, by adding a scanning direction control device and an image display control device to a scanning tunneling microscope, and by utilizing the original functions of the scanning tunneling microscope, By simply scanning the probe in different directions and creating and displaying images, it is possible to easily identify whether the tip shape of the probe is good or bad. Therefore, the shape of the tip of the probe can be quickly inspected after the probe is manufactured.

[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 an enlarged front view of an image display device, FIG. 3 is a flowchart for explaining an image creation method, and FIG. Figures 8 to 7 are partial front views showing examples of various tip shapes, Figures 8 to 11 are diagrams showing tunnel current generation states in various tip shapes, and Figure 12 is a conventional general scanning type. FIG. 2 is a block diagram showing the configuration of a tunneling microscope. [Explanation of symbols] 1... Scanning direction control device 2... Image display control devices 3 to 6... Image 101... Probe 102... Sample 103. ...Signal processing device 104...Scanning device 105...Scanning control device 106...Image storage device 107...Image display device

Claims (4)

[Claims] (1) A probe disposed close to the sample, a signal processing means for detecting tunneling current by applying a voltage between the probe and the sample, and a signal processing means for detecting tunneling current by applying a voltage between the probe and the sample; a scanning means for scanning the surface, a scanning control means for controlling the scanning of the sample surface by the probe performed via the scanning means, and data generated by the control of the scanning control means, and based on this data. A scanning tunneling microscope comprising an image storage means for creating and storing an image signal, and an image display means for displaying an image of the sample surface scanned by the probe based on the image signal created by the image storage means. scanning direction control means for performing scans in forward and reverse directions in at least one direction on the same area of the surface of the screen; and creating images corresponding to each of the forward and reverse scans, and displaying these images separately in the image display; A scanning type with a probe tip shape identification function, comprising an image display control means for displaying on the device, and identifying the tip shape of the probe by comparing a plurality of images displayed on the image display device. tunnel microscope. (2) In the scanning tunneling microscope with a probe tip shape identification function according to claim 1, the probe tip shape identification function is characterized in that the at least one direction is one of orthogonal X direction and Y direction. scanning tunneling microscope. (3) In the scanning tunneling microscope with a probe tip shape identification function according to claim 2, the image display device scans in each of the X positive direction, the X negative direction, the Y positive direction, and the Y negative direction. A scanning tunneling microscope with a probe tip shape identification function, which is characterized by displaying four images simultaneously. (4) Scan the same area on the surface of the sample in at least one direction with the probe in two scanning directions that are opposite to each other, create at least two images of the same area through this scanning, and Probe tip shape identification for a scanning tunneling microscope, characterized in that the tip shape of the probe is identified by displaying an image on at least one image display device and comparing the plurality of displayed images. Method.