JPH05322511A - Scanning measuring apparatus utilizing tunnel current - Google Patents

Abstract

PURPOSE:To achieve stable measurement and highly accurate measurement in a scanning measuring apparatus utilizing a tunnel current. CONSTITUTION:As a conductive probe 1 is brought close to the surface of a sample, a tunnel current is generated between the probe 1 and the sample. The measuring apparatus is so constituted as to measure the rough form of the surface of the sample by scanning the surface of the sample while the distance between the probe and the sample is controlled by the utilization of the tunnel current. Moreover, an insulating film 21 is provided at a leading end 1a of the probe 1. The thickness of the insulating film 21 is enough to prevent the field evaporation when the probe approaches the sample, more specifically, the thickness of the film 21 is the one of several atoms.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type measuring apparatus utilizing a tunnel current, and more particularly to a scanning type measuring apparatus utilizing a tunnel current suitable for measuring a fine shape of a sample surface.

[0002]

2. Description of the Related Art A scanning tunneling spectroscopic device is one example of a scanning measuring device utilizing a tunnel current. An example of a conventional scanning tunneling spectroscopic device is disclosed in Japanese Patent Application Laid-Open No. 3-2104.
No. 65. The scanning tunneling spectroscopic device is configured using the configuration of the scanning tunneling microscope. In a scanning tunneling microscope, the required voltage is applied between the conductive probe and the sample, and the probe and sample are brought close to each other at a minute distance so that a predetermined tunnel current flows between them, and the probe is placed on the sample surface. The height position of the probe is controlled so that the tunnel current is maintained at a constant value while scanning along. The scanning tunneling spectroscope has the following structure in the scanning tunneling microscope.
At each measurement point, stop the scanning operation of the probe and the servo control in the height direction of the probe, change the voltage applied between the probe and the sample, and measure the change in tunnel current with respect to the voltage change. Is composed of.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
More specifically, the probe is fixed to the tip of a cantilever attached to the fine movement mechanism, and the cantilever is displaced by the atomic force generated between the atom at the tip of the probe and the corresponding atom on the sample surface. To be configured.
Further, when a displacement occurs in the cantilever, a detection system for detecting the displacement is provided. When this detection system detects the displacement of the cantilever, the detection system sends the information to the control system, and the control system controls the position of the cantilever so that the distance between the probe and the sample becomes a predetermined constant distance. ..

As described above, in the scanning tunneling spectroscopic device disclosed in the prior art document, the displacement of the cantilever due to the interatomic force acting between the probe and the sample is detected, the position of the cantilever is adjusted, and Keep the distance between the samples constant.

The electric field generated between the probe and the sample is determined by the voltage applied between the probe and the sample and the distance between the probe and the sample. During scanning of the probe, when the distance control between the probe and the sample is not in time and the probe and the sample approach abnormally, the electric field generated between the probe and the sample becomes high depending on the applied voltage, This poses the problem that the atoms on the sample surface approaching the needle are field-evaporated, the sample surface is deformed, and the measurement accuracy is reduced.

An object of the present invention is to provide a scanning type measuring apparatus using a tunnel current with which measurement can be stably performed by preventing field evaporation and which has high measurement accuracy.

[0007]

A scanning type measuring apparatus using a tunnel current according to the present invention brings a conductive probe close to the surface of a sample, and causes a tunnel current to flow between the probe and the sample. The structure is such that the surface of the sample is measured by utilizing a tunnel current, and further, an insulating film is provided at the tip of the probe.

In the above structure, the thickness of the insulating film is preferably the thickness of several atomic layers.

[0009]

In the present invention, an insulating film having a thickness capable of passing a tunnel current is provided at the tip of the probe facing the sample surface, and the distance between the probe and the sample at which electric field evaporation does not occur is provided by this insulating film. This ensures a high accuracy and stable measurement.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, 1 is a conductive probe,
2 is a sample. For the sample 2, molybdenum disulfide (MoS2) is used, for example. The probe 1 is formed in the form of a cantilever. The tip 1a of the probe 1 is sharp,
It faces the surface of sample 2. The sample 2 is fixed on the base 3.

Reference numeral 4 denotes a fine movement mechanism. The fine movement mechanism 4 is composed of an X-axis piezoelectric element 4a, a Y-axis piezoelectric element 4b, and a Z-axis piezoelectric element 4c. The fine movement mechanism 4 can generate a three-dimensional displacement. The X-axis piezoelectric element 4a and the Y-axis piezoelectric element 4b constitute a scanning device that scans the probe 1 along the surface of the sample 2. The Z-axis piezoelectric element 4c is for changing the distance between the probe 1 and the sample 2. Fine movement mechanism 4
Has one end fixed to the base 5 and the other end fixed to the other end of the probe 1. The displacement sensor 6 is further attached to the other end. The displacement sensor 6 has a function of detecting the deflection of the probe 1 as a cantilever, and for example, a non-contact micro displacement meter using laser light is used.

Reference numeral 7 is a feedback control device, which inputs a signal detected by the displacement sensor 6 and gives a control signal obtained based on this signal to the Z-axis piezoelectric element 4c. Feedback control device 7
Controls so that the distance between the probe 1 and the sample 2 is maintained at a predetermined distance when the distance between the probe 1 and the sample 2 changes. In performing such control, the feedback control device 7 receives a command for control from the arithmetic control device 9 described later, and sends a signal detected by the displacement sensor 6 to the arithmetic control device 9 as necessary. For adjusting the distance between the probe 1 and the sample 2, the Z-axis piezoelectric element 4c is used.

Reference numeral 8 is an XY scanning control device. The XY scanning control device 8 receives a control signal from the arithmetic and control unit 9, controls the expansion / contraction operation of the X-axis piezoelectric element 4a and the Y-axis piezoelectric element 4b based on the control signal, and causes the probe 1 to perform a scanning operation.

In order to pass a tunnel current between the probe 1 and the sample 2, a voltage is applied between the probe 1 and the sample 2. 1
Reference numeral 0 is a voltage application control device for applying the voltage. The voltage application control device 10 sets an applied voltage based on a control signal given from the arithmetic and control unit 9. According to the voltage application control device 10, the applied voltage can be changed appropriately.

When a voltage is applied between the probe 1 and the sample 2 and the distance between them becomes a predetermined distance, a tunnel current flows. When a tunnel current flows between the probe 1 and the sample 2, this tunnel current is generated by the tunnel current detection device 11
Detected by. The detected tunnel current is given to the arithmetic and control unit 9.

Data for scanning the probe 1 is input and stored in the arithmetic and control unit 9 in advance. Further, in order to perform tunneling spectroscopic measurement, data for changing the applied voltage is input and stored. Based on such stored data, tunnel spectroscopic measurement is performed at each measurement point by changing the applied voltage and detecting the tunnel current value. The arithmetic and control unit 9 determines the position of each measurement point on the sample surface,
The relationship between each applied voltage and the tunnel current obtained by the measurement is displayed on the display device 12.

The operation of the scanning tunneling spectroscope having the above structure will be outlined. The probe 1 includes an X-axis and Y-axis piezoelectric device 4a, 4b for the X-axis and the Y-axis, which is formed by the arithmetic control unit 9 and the XY scanning control unit 8.
By controlling the operation of (1), the sample 2 is made to stand still on each measurement point on the scanning plane. At each measurement point, the arithmetic and control unit 9 controls the feedback controller 7 so that the displacement amount of the cantilever due to the interatomic force between the probe 1 and the sample 2 becomes a preset value. While the displacement amount is monitored by the displacement sensor 6, the expansion / contraction operation of the Z-axis piezoelectric element 4c is controlled. The arithmetic and control unit 9 changes the applied voltage between the probe 1 and the sample 2 via the voltage application controller 10,
The tunnel current detected by the tunnel current detection device 11 is input. Then, it moves to the next measurement point and repeats the same measurement operation.

FIG. 2 shows the tip 1a of the probe 1 in an enlarged manner. The tip 1 a of the probe 1 is covered with an insulating film 21. The thickness of the insulating film 21 is a thickness that allows a tunnel current to flow, and is a thickness that can secure a distance between the probe and the sample that does not generate an electric field that causes electric field evaporation with respect to an applied voltage. .. The thickness of the insulating film 21 is, for example, the thickness of several atomic layers. In this way, by providing the insulating film 21 on the tip portion 1 a of the probe 1, the tip portion 1 a
And the sample 2 do not approach at a distance smaller than the thickness of the insulating film 21. Therefore, destruction and deformation of the sample surface due to field evaporation do not occur, and highly accurate and stable tunneling spectroscopic measurement can be performed.

When molybdenum disulfide is used as the sample 2, 5.5 V / 0.3 nm (= 16.5 V / nm)
There is a report that electric field evaporation occurs with the electric field strength of (Japan Society for Opportunity Japan Mecha Life No. 27, 92-3, p4.
5). Usually, when performing the scanning tunneling spectroscopic measurement, the distance between the probe 1 and the sample 2 is about 1 nm, and the applied voltage between the probe and the sample is changed between −several volts and tens of volts. The electric field strength at this time is several V / nm, and electric field evaporation does not occur. Therefore, the thickness of the insulating thin film that covers the tip of the conductive probe needs to be 1 nm or less in order to pass the tunnel current.

In the above embodiment, the scanning tunneling spectroscope utilizing the scanning tunneling microscope has been described.
The configuration of the present invention can be generally applied to a measuring device that uses a tunnel current.

[0021]

As is apparent from the above description, according to the present invention, the tip of the probe is provided with the insulating film having a predetermined thickness. Therefore, the presence of the insulating film causes a gap between the probe and the sample. Since the minimum required distance is secured, destruction and deformation of the sample surface due to field evaporation do not occur, and highly accurate and stable measurements such as tunneling spectroscopy can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an enlarged view showing in detail a formation state of an insulating film on a tip portion of a probe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Probe 2 ... Sample 3, 5 ... Base 4 ... Fine movement mechanism 6 ... Displacement sensor 7 ... Feedback control device 8 ... XY scanning control device 9 ... Arithmetic control device 10 ... Voltage application control device 11 ... Tunnel current detection device 21 … Insulating film

Claims (2)

[Claims] 1. A measuring device in which a conductive probe is brought close to the surface of a sample, a tunnel current is passed between the probe and the sample, and the surface of the sample is measured by utilizing the tunnel current. A scanning measuring device utilizing a tunnel current, characterized in that an insulating film is provided at the tip of the. 2. The scanning measuring apparatus using a tunnel current according to claim 1, wherein the thickness of the insulating film is a thickness of several atomic layers. ..