JPH03229103A - Surface measuring instrument - Google Patents

Abstract

PURPOSE:To measure atomic arrangements by the same measuring instrument to resolution of 10<-1>Angstrom and to make a continuous scan over a wide range of >=1 mum by switching a voltage applied to a driving piezoelectric element for placing a probe in scanning operation in plural stages. CONSTITUTION:This surface measuring instrument consists of a probe scanning means 1 which places the probe 7 fitted to a microscope main body 6 in scanning operation and a micrometer 10 for finely adjusting the distance between a sample 9 supported on a sample support base 8 and the probe 7, and a power circuit 2 which applies the voltage to the piezoelectric element for driving the probe scanning means 1 is provided with a waveform generating circuit 3 and a high-voltage amplifier 5 through a changeover switch 4 so that they can be driven independently in an X, a Y, and a Z direction. The amplification factor of the voltage applied to respective piezoelectric elements for driving can be switched in plural stages, so when the power source output is made small when a narrow range is measured and made large when a wide range is measured to make a wide-range scan and measures an atomic level continuously by the sample measuring instrument.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a surface measurement device, and particularly to a surface measurement device such as a scanning tunneling microscope that measures the surface structure and surface electronic state of a solid. Regarding.

(Prior Art) A scanning tunneling microscope has been developed as a means of measuring each atom on the surface of a solid (Surface Science, Vol. 126, Page 236: G-Vinnitz (
G, Binnig)).

This involves scanning an electrically conductive probe with a sharp tip about 10 times above the surface of an electrically conductive solid sample.
By measuring the tunnel current, the structure and electronic state of the sample surface can be measured at the atomic level.

A piezoelectric element mechanically connected to the probe is used to scan the probe at about 10 A above the surface of the sample. A method is used in which a required number of pulses are applied to the piezoelectric element at a constant applied voltage to scan a predetermined distance. The displacement sensitivity of the piezoelectric element to the applied voltage can be selected by the shape of the piezoelectric element and the size of the electrodes. In a surface measuring device that scans a sample surface over a wide range (≧1 μm), it is necessary to use a piezoelectric element with high sensitivity. However, since the noise level of the circuit that generates the applied voltage determines the resolution of the surface measuring device, the resolution is sacrificed in such devices. That is,
When using a piezoelectric element with good sensitivity, even if there is a slight noise on the applied voltage with a constant waveform, the piezoelectric element will displace greatly, so it is difficult to scan a minute area with high precision. It becomes impossible.

On the other hand, piezoelectric elements with low sensitivity have been used in surface measuring devices whose purpose is to measure a narrow range at the atomic level. However, in this case, scanning over a wide range cannot be expected.

However, in a single surface measurement, it is often necessary to alternately measure the atomic level and scan a wide range on the sample surface.

For example, if the entire sample is not clean, or if the sample surface is scratched during 1ilFI measurement, it is necessary to interrupt the atomic level measurement and scan a wide range to find a clean part of the surface. There is.

Furthermore, when it is necessary to measure both large-scale structures and atomic arrangements, it becomes necessary to continuously perform scanning over a wide range and measurement at the atomic level.

(Quick problem to be solved by the invention) As described above, with conventional surface measurement devices such as scanning tunneling microscopes, in order to widen the scanning area, it is not possible to scan a minute area with high precision. On the other hand, there is a problem in that in order to scan a minute area with high precision, it is not possible to scan a wide range.

The present invention has been made in view of the above-mentioned circumstances, and has the ability to define 71'jll on the atomic scale with a resolution of approximately 10-1 people, and is capable of scanning a wide range of 1 μm or more. The purpose is to provide a measuring device.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in the present invention, the voltage applied to the drive piezoelectric element for scanning the probe can be switched in multiple stages.

Desirably, the amplification factor of the applied voltage can be switched in multiple stages, and the voltage applied to the driving piezoelectric element can also be switched in multiple stages.

(Function) According to the above configuration, since it is possible to switch the voltage applied to the piezoelectric element in multiple stages, the voltage applied to the piezoelectric element can be switched in a narrow range (10 to 10
08), the power supply output for scanning can be reduced, and when measuring a wide range, the power supply output can be increased. It becomes possible to perform level measurements continuously.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

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

In this scanning tunneling microscope, each power supply circuit 2 for applying voltage to an X-direction driving piezoelectric element 1 and a Y-direction driving piezoelectric element constituting a probe scanning means 1 is connected to a waveform generating circuit 3 and a changeover switch 4. and a high voltage amplifier 5 connectable to the high voltage amplifier 5.
The other parts are constructed in the same way as a normal scanning tunneling microscope. Here, the power supply circuit is an X-direction driven piezoelectric element.

Although they are provided independently for the Y-direction driving piezoelectric element and the Z-direction driving piezoelectric element, only one set is shown for the sake of simplification. Note that Z is used to control the distance between the probe and the sample.
A power supply circuit for the directional drive piezoelectric element is a waveform generation circuit 3.
You can look at it.

That is, a microscope body 6 is made of an invar alloy with a small coefficient of thermal expansion (an alloy made of iron containing iron, manganese, carbon, and other elements), and a probe scanning probe attached to the microscope body 6 and scanning a probe 7. A device comprising means 1 and a micrometer 10 having a sample support stand 8 at its tip and performing coarse movement of the distance between the sample 9 and the probe. The bidirectional driving piezoelectric element is constituted by a cylindrical piezoelectric element as shown in FIG. 2 (Review of Scientific Instruments, Vol. 57, p. 1688). This cylindrical piezoelectric element includes a cylindrical piezoelectric body 11 and an X electrode 12 formed oppositely on the outer surface of the piezoelectric body 11.
x, 13x, Y electrodes 12y, 13y formed opposite to each other at a position 906 rotations from the X electrode position along the outer surface, and a Z electrode 12 formed on the inner wall of the cylinder.
The power supply circuit 2 described above is connected between the X electrodes 12x and 13x and the Y electrodes 12y and 13y, and performs drive in the XY force direction, and the two electrodes 1
2z and the four electrodes 12x, 13x, 12y, 13y
A waveform generation circuit 3 is connected between the two. And X
By applying a voltage between the electrodes 12x and 13x, a piezoelectric effect is generated in the piezoelectric body, the spatial position of the probe fixed to the piezoelectric body in the X direction changes, and a voltage is applied between the Y electrodes 12y and 13y. By applying a voltage, the spatial position of the probe in the Y direction changes, and by applying a voltage between the Z electrode 12z and the four electrodes, the spatial position of the probe in the Z direction changes. The sensitivity of this piezoelectric element is 50 persons/■.

The waveform generation circuit has a maximum output voltage of 5V, but by passing the high voltage amplifier 5 through the switch 4, the maximum output voltage can be increased to 100V.
It is now possible to amplify the voltage by 500V.
It can cover a wide range.

For measurement, first, the graphite sample is placed on a sample support stand, and the distance through which the tunneling current flows (from the tip to the tip) is measured.
After roughly aligning the sample using the micrometer 10 to a distance of several samples, a voltage is applied to the two electrodes of the piezoelectric element to finely adjust the distance between the probe and the sample surface in two directions.

After this, the probe scanning means 1 is moved to the X direction driving piezoelectric element.

As a Y direction drive piezoelectric element, an X electrode 12x to be driven,
3(a) and 3(b) using the power supply circuit 2 described above between the 13x electrodes and the Y electrodes 12y and 13y, respectively.
) is applied.

At this time, the signal can be amplified 100 times by passing it through the high voltage amplifier 5 via the switch 4, and can cover a wide range up to a maximum amplitude of 500V. Then, the probe is scanned in the X direction according to the signal waveform shown in FIG. 3(a), the scanning speed and scanning width are determined, and the signal waveform shown in FIG. The interval between is determined.

In this way, by applying a predetermined signal, it is possible to scan the XY force direction probe parallel to the sample surface, measure the tunneling current at this time, and measure the atomic image on the sample surface.

In addition, when measuring the edges of the islands in a sample in which gold was deposited on the graphite surface to form islands with a diameter of about 100 people at an average spacing of 5000, first the X electrodes 12x, 13x
A voltage of 500V was applied through the high-voltage amplifier 5 by switching the switch 4 of the power supply circuit 2 between the Q and Y electrodes 12y and 13y, and scanning was performed over a wide area of 1 μm x 1 μm to obtain a flat and island distribution from the sample surface. Find a region where is uniform.

Subsequently, this region was
Observation is performed in a scanning range of 100 people x 100 people, and an area of 10 people x 10 suitable for observing the edge of the Au island is found from the obtained STM image.

After this, the X electrode 12 is centered around this found area.
The switch 4 of the power supply circuit 2 between the x and 13x electrodes and the Y electrodes 12y and 13y is switched, a voltage with a maximum amplitude of 2cm is applied, and 10 persons x 1 person is scanned to perform observation on the atomic scale. That is, FIG. 4 shows the results of measuring the voltage applied to the piezoelectric element by feeding back the tunnel current to the two electrodes 12Z and keeping the tunnel current constant during scanning. Here, V in the lateral direction, (voltage applied between the X electrodes)
, Vy (applied voltage between y electrodes) + V t in the vertical direction
(voltage applied between the z electrodes) was taken and plotted.

In this way, by performing both wide-range scanning and narrow-range scanning on the atomic scale, it becomes possible to perform highly accurate measurements extremely easily.

On the other hand, when attempting to perform measurements at the atomic scale without using a high-voltage amplifier, it was extremely rare for the edges of the islands to be captured in the scanning region.

In this example, the applied voltage is switched in both the X direction and the Y direction, but it goes without saying that it may be applied in either direction.

In addition, although this example describes a scanning tunneling microscope, the capacitance between the probe and the sample can be detected using a device similar to that shown in Figure 1 without being limited thereto. It can also be applied to other surface measurement devices such as a scanning capacitance microscope that measures the attraction and repulsion between the atoms of the probe and the atoms of the sample, such as an atomic force microscope that measures the attraction and repulsion between the atoms of the probe and the atoms of the sample.

〔Effect of the invention〕

As explained above, according to the surface measuring device of the present invention, since the voltage applied to the piezoelectric element for driving the probe can be switched in multiple stages, the same measuring device can It becomes possible to continuously scan a wide range and determine Ml at the atomic level.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a scanning tunneling microscope according to an embodiment of the present invention, FIG. 2 is a diagram showing its piezoelectric element, and FIGS. 3(a) and 3(b) are diagrams showing the output of a waveform generation circuit. , FIG. 4 is a diagram showing measurement results using the scanning tunneling microscope of the present invention. DESCRIPTION OF SYMBOLS 1... Probe scanning means, 2... Power supply circuit, 3... Waveform generation circuit, 4... Changeover switch, 5... High voltage amplifier, 6... Microscope body, 7... Exploration Needle, 8...
Sample support stand, 9 samples, 10...micrometer, No.! Figure 2 Voltage Vx Figure 4

Claims (1)

[Claims] A probe for surface measurement, a coarse movement mechanism for adjusting the distance between the probe and the sample surface, and a piezoelectric element for scanning the probe over the sample surface. A surface measuring device comprising: a drive means configured to measure the shape or physical properties of a sample surface while scanning the probe near the surface of the sample; a power supply circuit for applying voltage to the piezoelectric element; A surface measuring device characterized in that it is configured to be able to switch voltage in multiple stages.