JP2000065712A - Method for manufacturing silver probe of scanning tunnel microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable method for manufacturing the silver probe of a scanning tunnel microscope through the use of methyl alcohol as the solvent of an electrolyte, electrolytic grinding, and electrolytic etching. SOLUTION: A silver wire 4 is immersed in an electrolyte 2, and an A.C. voltage is impressed between the probe 4 and a parallel plate electrode 3 from an A.C. power source 5 to perform electrolytic grinding. This is automatically completed at a point of time when a part of the silver wire 4 immersed in the electrolyte 2 is completely dissolved. Next, the tip part of the probe 4 is returned in the electrolyte 2, and a D.C. voltage is impressed for a few seconds to perform electrolytic etching with the probe 4 as an anode. Finally, it is cleaned in methyl alcohol and naturally dried. Methyl alcohol is used as a solvent of the electrolyte 2. This is because methyl alcohol has a smaller surface tension and viscosity coefficient than water, and the tip part of the probe can be speedily isolated from the electrolyte 2 at the time of the completion of grinding.

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 (STM) device having an atomic resolution, and more particularly to a ST device.
The present invention relates to a method for manufacturing a silver probe used for obtaining spectroscopic knowledge of luminescence (STM luminescence) due to interaction between an STM probe and a measurement substance during M observation.

[0002]

2. Description of the Related Art There are, for example, the following techniques in such a field. (1) A. A. Gorbunov, B .; Wolf an
d J. Edelmann: Rev. Sci. Inst
rum. 64 (1993) 2393. (2) K. Dickmann, F.C. Demming a
nd J.J. Jersch: Rev. Sci. Instr
um. 67 (1996) 845. That is, in the above reference (1), a silver probe is manufactured by AC corrosion using a citric acid solution as an electrolytic solution.

Further, in the above-mentioned document (2), a silver probe is manufactured by direct current corrosion using aqueous ammonia as an electrolytic solution. In the probe manufacturing method (1), the probe corrosion process includes two steps. The first stage is shown in FIG.
The manufacturing apparatus shown in Fig. 1 is used. That is, a citric acid solution having a concentration of 40% is used as the electrolytic solution 101 in the electrolytic cell 100, and a silver wire (purity 99.9%) 1 serving as a probe is used.
03 and a flat plate electrode (made of stainless steel) as the opposite electrode
An AC voltage of 100 V is applied from an AC power supply 104 to the electrode 102 to perform electrolytic corrosion. In FIG. 5, reference numeral 105 denotes a probe holder.

Next, as a second step, as shown in FIG. 6, in order to reduce the curvature of the tip of the silver probe (purity 99.9%), an electrolytic solution 201 A 40% citric acid solution is dropped, a wire electrode (stainless steel wire) 202 is arranged in a semicircle, and a silver probe 203 is provided.
Is applied from the AC power supply 204 and electrolytic corrosion is performed again. At this time, the corrosion conditions such as the electrolytic solution and the applied voltage are the same as those in the first stage.

[0005] In the above-described probe manufacturing method (2),
Using a device as shown in FIG. 7, a silver wire (purity 99.9%) 303 serving as a probe is used as an anode and a flat plate electrode (made of stainless steel).
A direct current of 10 V is applied using 302 as a cathode to perform electrolytic corrosion. As the electrolyte 301, aqueous ammonia having a concentration of 10 to 35% is used. In addition, 300 is an electrolytic cell, 304 is a voltage control circuit, 305 is a probe holder, and 306 is a relay switch.

Here, for the purpose of reducing the curvature of the tip portion of the probe, although not described in detail, a voltage control circuit 304 is used to turn off the voltage applied between the probe anode and the stainless steel cathode simultaneously with the completion of electrolytic corrosion. Add functions.

[0007]

However, in the above-mentioned conventional method (1) for producing a probe, the resolution of a topographic image is at most about several nm, and the atomic resolution has not been obtained. Also in the probe manufacturing method (2), thermally decomposed highly oriented graphite (HOPG) is used only in the current image.
In contrast, only the atomic resolution was obtained, and the positional resolution of the topographic image was at most about 1 nm. These are considered to be due to the large curvature of the tip portion of the probe.

[0008] As described above, the use of the probe manufactured by the conventional technique does not provide electronic resolution in the STM observation with a silver probe which is considered to be effective for obtaining spectroscopic knowledge of STM emission. There were drawbacks. SUMMARY OF THE INVENTION The present invention provides a method for fabricating a silver probe for a scanning tunneling microscope with high reliability by using methyl alcohol as a solvent for an electrolytic solution and performing electrolytic polishing and / or electrolytic corrosion in order to solve the above-mentioned conventional problems. The purpose is to do.

[0009]

According to the present invention, there is provided a method for manufacturing a silver probe used in a scanning tunneling microscope, wherein methyl alcohol is used as a solvent for an electrolytic solution by electropolishing. It is designed to produce silver probes. (2) In a method for manufacturing a silver probe used in a scanning tunneling microscope, a silver probe is manufactured by electrolytic corrosion using methyl alcohol as a solvent for an electrolytic solution. (3) In a method for manufacturing a silver probe used in a scanning tunneling microscope, a silver probe is manufactured by combining electrolytic polishing and electrolytic corrosion using methyl alcohol as a solvent for an electrolytic solution. (4) In the method for producing a silver probe of a scanning tunneling microscope according to the above (1), (2) or (3), an electric field evaporation method in a scanning tunneling microscope arrangement is combined.

[0010]

Embodiments of the present invention will be described below in detail. FIG. 1 is a schematic view of an electrolytic polishing / corrosion apparatus for manufacturing a silver probe according to a first embodiment of the present invention.
In this figure, 1 is an electrolytic tank, 2 is an electrolytic solution (perchloric acid diluted 4 times with methyl alcohol), 3 is a parallel plate electrode, 4 is a silver wire used as a material for a probe, and 5 is an AC power supply. , 6
Is a DC power supply, and 7 is a probe holder.

A silver wire (purity: 99.99%) 4 having a diameter of 0.5 mm is used as a material for the probe, and a perchloric acid (HClO ₄ ) diluted four-fold with methyl alcohol is used as an electrolytic solution 2. . For the purpose of making the electric field applied to the probe uniform, two stainless steel plates (parallel plate electrodes) are used as the counter electrode 3, and the silver wire 4, which is a material for the probe, can be arranged in the middle. A mechanism capable of manually adjusting the position of the probe holder 7 is provided.

First, a silver wire 4 is immersed in the electrolytic solution 2 by about several mm, and a 19 V AC power is applied between the probe 4 and the parallel plate electrode 3.
Is applied to perform electropolishing. This automatically ends when the portion of the silver wire 4 immersed in the electrolytic solution 2 is completely melted.
Next, the tip portion of the probe 4 is returned into the electrolytic solution 2, and 5 V DC is applied from the DC power supply 6 for several seconds using the probe 4 as an anode to perform electrolytic corrosion. Finally, it is washed in methyl alcohol and air dried. The results of STM observation using the silver probe obtained by the above-described operation are shown below.

FIG. 2 is a topographic image when HOPG is used as a sample, and shows that atomic resolution was obtained. This indicates that the use of methyl alcohol as the solvent for the electrolytic solution is effective for improving the quality of the probe. The scanning conditions for observing the topographic image were a bias voltage of 0.05 V (positive on the sample side) and a tunnel current of 1
nA.

Next, a second embodiment of the present invention will be described. In this embodiment, the operation of the first embodiment is added to the operation of the field evaporation in the STM arrangement. The procedure of electrolytic polishing and corrosion of the silver probe is the same as that of the first embodiment. FIG. 3 is a schematic view of an electric field evaporation method in an STM arrangement showing a second embodiment of the present invention.

In this figure, 11 is a sample surface, 12 is a probe (feedback on) during scanning, 13 is a probe (feedback off) when a high bias is applied, and 14 is a position where electric field evaporation is performed. In this embodiment, an n-type silicon single crystal substrate (plane orientation <111>) having a resistivity of about 0.5 Ωcm is used as a sample. First, the probe was scanned at a scanning speed of 10 under the conditions of a bias voltage of −2 V and a tunnel current of 2 nA.
Scan at 0.6 nm for 00 nm / s.

Next, after the scanning of the probe is interrupted and the feedback is turned off 13, a pulse voltage of −10 V is applied between the probe and the sample for 210 μs. Thereafter, the operation of turning on the feedback 12 and restarting the scanning is repeated 40,000 times. FIG. 4 shows observation results of topographic images before and after the electric field evaporation operation in the STM arrangement. As shown in FIG. 4A, the state of the tip of the topographic image before the electric field evaporation operation is unstable, and it is difficult to obtain atomic resolution. This indicates that electrolytic polishing (corrosion) alone is not enough to obtain atomic resolution for silicon.

On the other hand, after the electric field evaporation operation, as shown in FIG. 4 (2), there is an advantage that it has an atomic resolution and a 7 × 7 rearranged structure can be observed in a topographic image. The scanning conditions at the time of observing the topographic image are bias voltage 2
V, the tunnel current is 2 nA. According to the present invention, as described above, methyl alcohol is used as a solvent for the electrolytic solution. This is because methyl alcohol has a smaller surface tension and a lower viscosity coefficient than water, and can quickly separate the tip of the probe from the electrolyte at the end of polishing.

Further, by combining electrolytic polishing with alternating current and electrolytic corrosion with direct current, compounds generated on the surface of the probe in the electrolytic solution are removed. In addition, STM
Electric field evaporation in the arrangement is performed to remove projections considered to be caused by non-uniformity of the reaction during electrolytic polishing and corrosion, and to sharpen the probe portion. That is, the operation of turning off the feedback during the scanning of the probe and applying a pulsed high bias voltage between the probe and the sample is repeated.

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0020]

According to the present invention, the following effects can be obtained. (A) Methyl alcohol having a smaller surface tension and a lower viscosity than water is used as a solvent for the electrolytic solution. Thus, the tip of the probe can be quickly separated from the electrolytic solution at the end of polishing.

(B) By combining the electrolytic polishing with alternating current and the electrolytic corrosion with direct current, it is possible to remove the compound formed on the probe surface in the electrolytic solution.
In other words, it is possible to manufacture a silver STM probe capable of observing an industrially important silicon surface with an atomic resolution by using an electropolishing method using AC, an electrolytic corrosion method using DC, or a combination of both using methyl alcohol as a solvent for an electrolytic solution. it can.

(C) By performing the electric field evaporation in the STM arrangement, it is possible to remove a projection which is considered to be caused by the non-uniformity of the reaction at the time of electrolytic polishing and corrosion, and to sharpen the tip portion of the probe. That is, by repeating the operation of turning off the feedback during the scanning of the probe and applying a pulsed high bias voltage between the probe and the sample, the tip of the probe can be sharpened. In other words, by adding an STM field-evaporation method that can easily obtain a high electric field, it is possible to observe an industrially important silicon surface with atomic resolution, and to use a silver STM with a sharpened tip of the probe. A probe can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view of an electrolytic polishing / electrolytic corrosion apparatus for manufacturing a silver probe according to a first embodiment of the present invention.

FIG. 2 is a topographic image when HOPG is used as a sample.

FIG. 3 is a schematic diagram of an electric field evaporation method in an STM arrangement showing a second embodiment of the present invention.

FIG. 4 is a diagram showing observation results of topographic images before and after an electric field evaporation operation in an STM arrangement.

FIG. 5 is a schematic view of a conventional electrolytic corrosion apparatus for manufacturing a silver probe.

FIG. 6 is a schematic view of a conventional electrolytic corrosion apparatus for manufacturing a silver probe.

FIG. 7 is a schematic view of a conventional electrolytic corrosion apparatus for manufacturing a silver probe.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Electrolyzer 2 Electrolyte (Perchloric acid diluted 4 times with methyl alcohol) 3 Parallel plate electrode 4 Silver wire used as a material of a probe 5 AC power supply 6 DC power supply 7 Probe holder 11 Sample surface 12 Scanning Probe (feedback on) 13 Probe when high bias is applied (feedback off) 14 Electric field evaporation position

Claims (4)

[Claims] 1. A method for manufacturing a silver probe for use in a scanning tunneling microscope, wherein the silver probe is manufactured by electropolishing using methyl alcohol as a solvent for an electrolytic solution. Production method. 2. A method for producing a silver probe for use in a scanning tunneling microscope, wherein the silver probe is produced by electrolytic corrosion using methyl alcohol as a solvent for an electrolytic solution. Production method. 3. A method for manufacturing a silver probe for use in a scanning tunneling microscope, wherein the silver probe is manufactured by combining electrolytic polishing and electrolytic corrosion using methyl alcohol as a solvent for an electrolytic solution. How to make a silver probe for a tunnel microscope. 4. The method for producing a silver probe of a scanning tunnel microscope according to claim 1, 2 or 3, wherein an electric field evaporation method in a scanning tunnel microscope arrangement is combined.