JPH05180615A - Scanning tunneling microscope - Google Patents

Abstract

PURPOSE:To prevent that a tunnel current comes not to flow due to the abrasion of gold deposited on the surface of a guide 8 which guides a table 9 holding a sample thereon in a double bobbin-type scanning tunneling microscope. CONSTITUTION:A guide 8 is formed of invar. Invar used here is an alloy including iron and having a considerably small thermal expansion coefficient at normal temperatures. Invar composed of 64% iron and 36% nickel in the weight ratio, super invar composed of 64% iron, 30-32% nickel and 4-6% cobalt, or an alloy of stainless and invar composed of 53-54% cobalt, 9-10% chromium and 36-37% iron may be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning tunneling microscope.

[0002]

2. Prior Art The 1988 American Institute of Physics
of Physic, pp. 1897-1902, by the University of Illinois, scanning tunneling microscope using double bobbin piezo (hereinafter referred to as STM. STM stands for Scanning Tun
Neling Microscope) is proposed. The inventors of the present invention have prototyped this double bobbin type STM. This ST
M is shown in FIG. This STM is excellent in that it is extremely compact and is not easily affected by the atmosphere such as vibration and heat.

The structure of the double bobbin type STM shown in FIG. 1 will be described. A disc-shaped Macor plate 3 is fixed to a vertical surface of a base 1 having an L-shaped cross section via a disc-shaped isolation 2. An outer piezo bobbin 4 for sample approach and an inner piezo bobbin 5 for XY scanning are arranged on the macor plate 3. A probe 6 is attached to the inner piezo bobbin 5, a sample base 7 is attached to the outer piezo bobbin 4, and a guide 8 for guiding a table 9 on which a sample is placed is attached to the sample base 7.

The principle of operation of this double bobbin type STM will be briefly described. The table 9 on which the sample is placed brings the sample closer to the probe 6 by inputting a sawtooth wave to the outer piezo bobbin 4 and stops the approaching operation at the same time when the tunnel current flows. Next, the probe 6 is scanned on the sample by the inner piezo bobbin 5 to form an image of the shape of the electron cloud on the sample surface.

By the way, as the guide 8 for guiding the table 9 on which the sample is placed, there is used a quartz rod having a low coefficient of thermal expansion on which gold (Au) is vapor-deposited. The guide 8 has a function of passing a tunnel current and a function of performing fine movement feeding by applying a stick slip by a sawtooth wave.

[0006]

However, since evaporated gold is soft, it is
When the table 9 rubs against it, it is greatly worn, and when the sample approach is repeated one after another using a table on which various samples are placed, there is a problem that the tunnel current stops flowing. Therefore, there is also a problem that the sample does not stop at a position about 10 angstroms away from the tip of the probe 6 where the tunnel current flows, and the probe 6 and the table 9 on which the sample is placed collide. As a result, there is a problem that the scanning tunneling microscope cannot be used after repeated use many times.

The present invention has been made in order to solve the above-mentioned conventional problems. Even if the sample is used a large number of times, conduction failure of the tunnel current does not occur. Another object of the present invention is to provide a scanning tunneling microscope that can be stopped at the position where the light flows and can reliably perform subsequent operations.

[0008]

In order to solve the above-mentioned problems, the present invention has a base to which a macol plate is fixed via isolation, and an external piezobobin for sample approach is fixed on the macol plate. And an internal piezo bobbin for XY scanning is installed,
A probe was connected to the inner piezo bobbin and a sample base was connected to the outer piezo bobbin, and in the scanning tunneling microscope equipped with a guide for guiding a table on which the sample was placed, the guide was an amber alloy.

Here, the amber alloy means an alloy containing iron having a very small coefficient of thermal expansion at room temperature.

[0010]

[Function] Since the guide is made of amber alloy,
Even when it is used many times, the conduction failure between the guide and the sample table does not occur.

Further, since it is an amber alloy, the coefficient of thermal expansion is small, and it is possible to minimize the fine movement of the sample table thereon due to expansion and contraction of the guide due to temperature changes.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. Figure 1 shows a conventional double bobbin type STM.
FIG. 1 is a perspective view illustrating the structure of the present invention, but the present invention is one in which the material of the guide is changed. Therefore, FIG. 1 shows an embodiment of the double bobbin type STM of the present invention by changing the material of the guide. Is a perspective view showing.

In FIG. 1, an L-shaped base 1 is made of duralumin, which is lightweight and has high durability, and a Macor plate which is an insulating material is formed on a vertical surface of the base 1 through a POM isolation 2. 3 is fixed by bolts or the like. An outer piezo bobbin 4 for approaching the sample and an inner piezo bobbin 5 for XY scanning are arranged on the Macor plate 3. A probe 6 is connected to the inner piezo bobbin 5 on the side opposite to the Macor plate 3 side.

Next, a sample base 7 made of duralumin is connected to the outer piezo bobbin 5 on the side opposite to the Macor plate 3 side. Then, two rod-shaped guides 8 for guiding a table 9 (see FIG. 2) on which the sample 10 is placed are attached in parallel to the sample base 7.

The guide 8 is made of Invar alloy. The guide rod 8 is solid or hollow and is entirely made of an amber alloy, and is fixed to the sample base 7 using a conductive thermosetting adhesive. Here, the amber alloy refers to an alloy containing iron having a very small coefficient of thermal expansion at room temperature. Iron: Nickel = 64%:
A so-called amber alloy having a 36% weight ratio composition is easily available and has a thermal expansion coefficient of 0.9 × 10 −6.
/ ° C., which is a value close to the thermal expansion coefficient of the quartz rod of 0.5 × 10 −6 / ° C., and the same low thermal drift as in the case of the conventional example in which the quartz rod is used for the guide can be used. 8 useful materials. Also, iron: nickel: cobalt = 6
Since the super-amber alloy having a weight ratio composition of 4%: 30 to 32%: 4 to 6% has a coefficient of thermal expansion of ± 0.1 × 10 −6 / ° C., it can have a further low thermal drift. .. Also, cobalt: chromium: iron = 53 to 54%: 9 to 10
The stainless steel amber alloy having a weight ratio composition of 36: 37% has a coefficient of thermal expansion smaller than that of the amber alloy, and has high corrosion resistance, and can be used in the present invention.

Next, the scanning method of the double bobbin type STM of the present invention will be described with reference to FIGS. 2 and 3
In FIG. 3, the inner piezo bobbin 5 is originally projected so as to be easily drawn.

First, referring to FIG. 2, when the sample approach is performed, the probe 6 is positioned in advance under the microscope at a position where the probe 6 comes, and the sample 9 is mounted on the table 9 on which the sample 10 is mounted. Set on top of 8.

Next, from the non-energized state of FIG. 2, to FIG.
As shown in (B), a sawtooth voltage is applied to the outer piezo bobbin 4 while monitoring the tunnel voltage, and the table 9 on which the sample is placed is pulled toward the probe 6 side while causing stick-slip. That is, when the outer piezo bobbin 4 is momentarily extended, the table 9 on which the sample is placed does not move due to slip (FIG. 3 (A)). Since it is pulled toward the needle 6 side (FIG. 3 (B)), by repeating this operation, the table 9 on which the sample is placed is gradually pulled toward the probe 6 side.

Then, the table 9 on which the sample is placed and the probe 6
Is approaching to the limit and a tunnel current flows between the surface of the sample 10 and the probe 6, and at the same time, the voltage supply to the outer piezo bobbin 4 is stopped and the table 9 on which the sample is placed is stopped. At the same time, the voltage of the inner piezo bobbin 5 is applied to contract the inner piezo bobbin 5 to prevent the probe 6 from colliding with the sample 10. Since the guide 8 is made of amber alloy, it is possible to reliably lengthen the tunnel current even when the guide 8 is already used many times, and therefore, to stop the voltage supply to the outer piezo bobbin 4 thereafter. Immediate voltage application to the inner piezo bobbin 5 can be reliably performed.

Thereafter, a voltage is gently applied to the inner piezo bobbin 5, and when the tunnel current flows again, the voltage applied to the inner piezo bobbin 5 is held. In this state, the system becomes standby, and the portion to be analyzed is XY-scanned using the inner piezo bobbin 5, and the driving voltage of the inner piezo bobbin 5 is amplified to image the shape of the electron cloud on the surface of the sample 10. Since the guide 8 is formed of an amber alloy, the temperature drift is small, so that the expansion and contraction of the guide 8 due to the temperature change during scanning is sufficiently prevented, and therefore the table 9 on which the sample is placed.
Is prevented from moving. Further, since the amber alloy has good corrosion resistance, the guide 8 can always flow a stable tunnel current without causing rust or the like on the surface even after the STM has been manufactured for a long time. With these, a good image can be obtained.

[0021]

According to the present invention, the guide of the table on which the sample is placed is made of amber alloy. Therefore, even when the scanning tunneling microscope is used many times, good continuity between the table and the guide can be maintained. The tunneling current can be passed to operate the scanning tunneling microscope satisfactorily.

Further, since the amber alloy is used for the guide, the temperature drift can be reduced and a good scanning image can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of a scanning tunnel microscope of the present invention and a conventional scanning tunnel microscope.

FIG. 2 is a principle diagram of the operation of the scanning tunneling microscope of the present invention when the piezoelectric element is not energized.

FIG. 3 is an operation principle diagram of the scanning tunneling microscope of the present invention in a piezoelectric energized state.

[Explanation of symbols]

 1 base 2 isolation 3 macol plate 4 outer piezo bobbin 5 inner piezo bobbin 6 probe 7 sample base 8 guide 9 table 10 sample

Claims (1)

[Claims] 1. A base is provided with a macor plate fixed to the base via isolation, and an outer piezo bobbin for sample approach and an inner piezo bobbin for XY scanning are disposed on the macor plate.
A probe is connected to the inner piezo bobbin and a sample base is connected to the outer piezo bobbin, and in the scanning tunnel microscope equipped with a guide for guiding the table on which the sample is placed, the guide is made of amber alloy. A scanning tunneling microscope.