JPH1126273A - Manufacture of metallic material provided with surface controlled at atomic level - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metallic material provided with a surface controlled at an atomic level. SOLUTION: Adsorption species are strongly adsorbed by a metal surface, and the metal surface is soaked in an electrolytic solution as an acting pole, and the potential at which the metal surface is electrolytically etched and the adsorption species is held on the metal surface is applied to the metal surface, and the metal surface is electrolytic-etched in the electrolytic solution, while an adsorption layer is held. Or, by applying the potential, at which a solute metal is electrolytically deposited and the adsorption species is held on the metal surface, to the metal surface with the metal surface on which the adsorption species is held as an acting pole, a solute metal is electrolytically deposited on the metal surface. Thereby electrolytic etching or electrolytic deposition is performed on the metal surface while the adsorption species is held, so that a specific index number surface is inactivated with the adsorption species, and a surface planarized at an atomic level and a surface in which only a specific step direction appears are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic recording material, a sensor, a catalyst material,
The present invention relates to a method for manufacturing a metal material suitable for a battery material, wiring on a printed circuit board, and the like.

[0002]

2. Description of the Related Art A recording medium of a magnetic disk device used as a recording medium of a computer or the like has been reduced in thickness. In recent years, a sputter disk by a dry process, a plating disk by wet plating, and the like have been used. In addition, the density of the recording medium has been increased in response to the need for a high recording capacity, and the size of the apparatus has been reduced, such as narrowing the head / disk, further reducing the thickness of the recording medium, and reducing the thickness of the head. Is being promoted. For example, the thickness of a thin-film disk is 0.06 μm, the spacing between the head and the disk reaches a level of about 0.2 μm, and the order of the control technology extends to the sub-micron level. As a result of such miniaturization, the surface of the disk itself must be a flat surface on the order of the same level or less, because the presence of surface defects and excessive roughness will adversely affect the magnetization in the minute area. Is required.
Further, further miniaturization is required in order to meet the needs for higher density of the recording medium in the future, and the surface flatness of the sub-nano order is also desired for the surface of the recording medium.

[0003] In printed circuit boards on which various elements are mounted and interconnected in the field of electronic equipment, miniaturization of the equipment itself,
Techniques such as fine wiring and high multilayer wiring are important in response to needs for higher performance and higher functionality. For example, when mounting various components such as LSIs, in recent years, surface mounting in which components are directly mounted on the surface of a substrate is mainstream. , Pin pitch reduction, and the like. In order to meet the needs for further downsizing and higher performance in the future, it is necessary to develop fine processing technology for wiring materials such as Cu. Further, surface microfabrication at the atomic level becomes even more important for improving the contact between the wiring at the mounting location and the pin of the component, and increasing the wiring density by miniaturizing the wiring at the wiring portion.

In recent years, studies on surface reactions at the atomic level in the field of catalytic reactions and the like have revealed that the reactions greatly change depending on the surface conditions. For example, studies using single crystal metals have shown that catalytic activity is completely different on surfaces with different exponential planes, and that catalytic reactions can be controlled by introducing surface adsorbed species. In this regard, if a method of exposing a specific index plane with atomic level flatness is established, the catalytic reaction can be controlled by controlling active sites and introducing adsorbed species based on the surface, and a highly functional catalyst can be obtained. It is expected to be obtained. In the case of sensors and electrode materials, since the reaction field is the surface of each material, the processing technology at the atomic level on the material surface becomes important as in the case of the catalyst material. For example, in the case of a secondary battery, one of the issues for improving the battery life is suppression of dendrite generation. Therefore, when the electrode surface is flattened at the atomic level, the electrolytic deposition reaction site is homogenized, and an electrode shape effective for suppressing dendrite can be obtained.

[0005]

In order to expose a surface having atomic level flatness, annealing is usually performed in an ultra-high vacuum or a reducing gas atmosphere after finishing by mechanical polishing. . However, when using cobalt, iron, or the like as a base material, it is necessary to anneal at a temperature lower than the phase transformation point, and it is not possible to perform treatment in a temperature range effective for surface flattening. Furthermore, in the high-temperature treatment, impurity elements such as sulfur contained in the material diffuse to the surface and remain on the surface during the cooling process, so that a surface layer in which impurities are concentrated is easily generated on the material surface. The impurity-enriched layer may form a compound during the cooling process after annealing. For this reason, it is very difficult to produce a clean and atomically planarized surface by the annealing method. Therefore, in the treatment in an ultra-high vacuum, impurities accumulated on the surface are released into a vacuum by ion sputtering using Ar ions or the like, and the surface roughened at the atomic level as a result of sputtering is planarized by annealing. The method has been adopted. However, even when annealing is performed again, diffusion and accumulation of impurities such as sulfur still occur, so that it is necessary to repeat sputtering and annealing in a considerable cycle.

When the material surface is planarized at the atomic level,
The effect of the surface oxidation of the material is significant. Usually iron,
The surface of a metal material such as nickel and cobalt is always covered with an oxide film having a thickness of about several tens angstroms in the air. To obtain a clean surface, it is first necessary to completely remove the oxide from the material surface. However, since the surface of this kind of material has a very high reaction activity to oxygen, the process of flattening the surface at the atomic level uses an ultra-high vacuum to avoid contact with oxygen, and removes oxygen species on the surface. Therefore, a method of treating in a reducing gas atmosphere is required. As a result, in order to industrially perform the flattening at the atomic level, a device capable of controlling the atmosphere is required, and it is inevitable that the equipment becomes complicated, large in scale, and high in cost.

As a method for obtaining a flat metal surface relatively easily, electrolytic etching is employed. Conventional electrolytic etching performed under normal conditions is effective for obtaining a metallic glossy surface at a macro level. However, when the etched surface is viewed on the order of nanoscale, it is very rough, and it is difficult to obtain a surface controlled at the atomic level by electrolytic etching. The present invention has been devised to solve such a problem, and performs a complicated and large-scale process by performing electrolytic etching or electrolytic deposition on a metal surface holding an adsorption layer under a potential-controlled condition. It is an object of the present invention to provide a metal surface which is flattened at an atomic level without requiring special equipment and is suitable as a magnetic memory material, a sensor, a catalyst material, a battery material and the like.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for producing a metal material having a surface controlled at an atomic level by electrolytic etching. Immerse in the electrolyte solution with the surface as the working electrode,
It is characterized in that a potential at which the metal surface is etched while the adsorbed species is held is applied to the metal surface, and the metal surface is electrolytically etched in an electrolyte solution while the adsorbed layer is held. When producing a metal material with a surface controlled at the atomic level by electrolytic deposition, the adsorbed species was strongly adsorbed on the metal surface, the metal surface was immersed in the electrolyte solution as the working electrode, and the adsorbed species was retained. Apply a potential to the metal surface to the metal surface as it is,
The solute metal is electrolytically deposited on the metal surface in the electrolyte solution while holding the adsorption layer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an adsorbed species is strongly adsorbed on a metal surface, and electrolytic etching or electrolytic deposition is performed in an electrolyte solution while holding the adsorbed layer. The type of the base metal is not particularly limited.
Seeds, alloys of two or more kinds, alloys with semimetals, and the like are used. In order to flatten the metal surface at the atomic level, it is effective to mechanically polish the base metal prior to electrolytic etching or electrolytic deposition so as to expose a specific target index surface. Examples of adsorbed species include halogen, halide ions, sulfur, sulfate ions, nitrate ions, phosphate ions, cyanide, cyanide ions, thiocyanate, thiocyanate ions, and carbon monoxide. May be. The adsorption amount of the adsorbed species does not particularly limit the present invention, and is set so that the adsorbed species is held on the metal surface in a range of a monoatomic layer or several atomic layers. The coverage is not particularly limited as long as the activity for dissolution or electrolytic deposition of the metal surface can be suppressed.

The method of holding the adsorbed species on the metal surface is not particularly limited. For example, a method of immersing the base metal in a solution in which the adsorbed species is dissolved as an ion, Any of a liquid phase method and a gas phase method, such as a method of bringing into contact with a base metal by introducing into a substrate, can be adopted. The amount of the adsorbed species may be controlled by heating the metal surface, adjusting the pressure of the adsorbed gas, or the like. In the present invention, the fact that the adsorbed species is adsorbed on the surface by the strong binding energy held on the surface of the substrate even in the process of dissolving the substrate in the anode or in the process of cathode deposition is referred to as strong adsorption.
As the electrolyte solution for dissolving or electrolytically depositing the metal surface, various solutions such as a solution using water or an organic substance as a solvent, a molten salt of the electrolyte itself, and the like are not limited. The electrolyte solution does not necessarily need to contain the component of the adsorbed species in the solution. Further, the ion concentration of the target metal in the electrolyte solution is not particularly limited. For example, even if the metal ion concentration is zero, the metal ions eluted by electrolytic etching are used for electrolytic deposition, so that the surface of the base metal is smoothed at the atomic level by repeating electrolytic etching and electrolytic deposition. . Solute concentration, p
Electrolysis conditions such as H, bath temperature, electrode area, and amount of electricity are not particularly limited, and are appropriately set according to an electrolytic etching reaction, an electrolytic deposition reaction, and the like.

When the adsorbed species is adsorbed on the metal surface in the liquid phase,
It is also possible to control the potential of the metal surface by immersing the base metal as an electrode in a solution containing the components of the adsorbed species. This method is an effective method because adsorption can be controlled more accurately and easily. In this case, the base metal is coated with the adsorbed species prior to the electrolytic treatment. In the liquid phase adsorption, by introducing the adsorbed species into the electrolyte during the electrolytic treatment, the adsorbed species can be coated on the metal surface in the same solution system in which the electrolytic treatment is performed. Liquid phase adsorption is more preferable in that the equipment can be simplified. When electrolytic etching or electrolytic deposition of the base metal while holding the adsorption layer, it is important to use the base metal as the working electrode in the electrolyte solution and to precisely control the electrode potential of the working electrode. That is, retention and desorption of the adsorbed species on the metal surface are controlled by the potential of the base metal, and electrolytic etching and electrolytic deposition are similarly controlled by the potential of the base metal. Therefore, the combination of the base metal and the adsorbed species is selected so that the potential range suitable for electrolytic treatment of the base metal and the potential range in which the adsorbed species is held overlap.

Although the electrode potential varies depending on the combination of the base metal and the adsorbed species, the potential at which the adsorbed species is held in advance by an electrochemical method such as a cyclic voltammogram and the potential at which the base metal is dissolved or electrolytically deposited. Is confirmed, and the electrode potential can be determined based on the result. When the adsorbed species is adsorbed on the surface of the base metal, the movement of the electrons caused by the adsorption is observed as a current peak on a cyclic voltammogram. From this peak, the potential at which the adsorbed species is held can be confirmed. Further, the presence of the adsorbed species can be confirmed by observing the surface when the potential is directly changed on an atomic scale using an electrochemical scanning tunneling microscope (STM). The potential at which the anode dissolution of the substrate starts can be confirmed from the position where the anode current rises on the cyclic voltammogram. Some metals may be passivated or have their surface immediately covered with oxide, with little anodic dissolution. Therefore,
In order to grasp the surface state in more detail, it is preferable to observe using a STM.

The potential at which electrolytic deposition occurs is usually lower than the potential at which the anode is dissolved, and is automatically determined according to the anode dissolution potential. The potential controlled in the planarization of the base varies depending on the type of metal, but is generally 0.2 V higher than the open circuit potential.
The following noble potential is set as the upper limit. The open circuit potential is a potential as measured without a circuit connected, while the electrode is immersed, and corresponds to the immersion potential. If the potential becomes a noble potential exceeding 0.2 V from the open circuit potential, the substrate is severely dissolved, the surface irregularities become large, and it becomes difficult to obtain a flat surface at the atomic level. On the other hand, the lower limit electric potential at the time of electrolytic deposition is not particularly limited, but is set at least in a region lower than the electric potential at which the oxide is reduced and removed. This potential is
Although it depends on the type of metal, it is determined by a technique such as cyclic voltammogram. In the cyclic voltammogram, a cathode peak is observed as the oxide is reduced, and the reduction potential of the oxide is determined from the peak position.

During the electrolytic etching or electrolytic deposition, the surface state of the substrate metal being processed and the state of the adsorbed species are determined by STM.
Observes the surface state at the atomic level. Therefore, effective condition setting can be performed by STM observation. The base metal having a surface flattened at the atomic level by the electrolytic treatment is taken out of the electrolyte solution while holding the adsorbed species or after desorbing the adsorbed species,
Used as a material for various applications. When the adsorbed species is desorbed in the electrolyte solution, the adsorbed species is desorbed by holding the base metal in a sufficiently low region in the electrolyte solution.

[0015]

The adsorbed species strongly adsorbed on the surface of the base metal is adsorbed again on the newly exposed metal surface under conditions where the metal can be adsorbed, even if the underlying metal is dissolved. In addition, since the adsorption energy between the metal surface and the adsorbed species is slightly different depending on the exponential plane, if the energy state of the metal surface can be finely controlled by controlling the potential, the adsorbed species is preferentially retained on a specific exponential plane. Can be made a situation. When a metal is electrolytically etched under these conditions, when a specific index surface is exposed, the surface is covered with the adsorbed species. Therefore, the activity of the metal surface is lost by the adsorbed species, and the metal surface is etched only from active sites such as kinks and steps. Then, the exposed metal surface gradually becomes only a specific index surface holding the adsorbed species as the electrolytic etching progresses, and the number of dissolution active sites such as steps decreases. As a result, a flat surface at the atomic level can be exposed over a wide range. In addition, when electrolytic deposition is performed while retaining the adsorbed species, the phenomenon completely opposite to that of electrolytic etching, that is, the step edge acts as a deposition site rather than on the terrace that retains the adsorbed species, so that a flat surface at the atomic level is generated. It is formed.

On the other hand, when electrolytic etching or electrolytic deposition is performed on a metal surface on which the adsorbed species is not retained, even if the amount of etching or the amount of deposition is controlled by controlling the potential, the activity in the exposed terrace surface is reduced. Is higher than the metal surface holding. Therefore, melting and precipitation occur on the terrace, and it becomes very difficult to expose a flat terrace at the atomic level. Further, the step directions appearing in the electrolytic etching and the deposition process are not linear, and it is impossible to make the directions uniform. The amount of metal surface etching and the amount of electrolytic deposition are controlled by adjusting the potential. for that reason,
It is possible to create a surface state with a specific step density, not just an atomically flat surface. In this case, it is preferable to perform electrolytic etching or electrolytic deposition while observing the surface state by STM.

When the metal surface holding the adsorbed species is electrolytically etched, the direction of the atomic arrangement of the adsorbed species becomes more stable, so that the step direction appearing in the electrolytic etching process becomes parallel to the atomic arrangement of the adsorbed species. By utilizing this phenomenon, a metal surface having only steps in a specific direction can be formed. That is, it is possible to perform electrolytic etching and electrolytic deposition controlled at the atomic level, for example, by making the shapes of the step lines uniform. In a specific index plane, anisotropy occurs in step lines in different directions formed on the metal surface depending on the adsorbed species. For example, on the fcc metal (100) surface, c (2 ×
When iodine or the like is adsorbed at the position 2), the step of the height of a single atom formed on the (100) plane is in two directions [010] and [001] parallel to the atomic row of the adsorbed species. . In the two orthogonal steps, as shown in FIG. 1, the structures of the adsorbed species and the underlying metal of the upper terrace and the lower terrace through the step are different. When such a surface is subjected to electrolytic etching or electrolytic deposition, the reaction activity in steps in two different directions is not isotropic, so that a metal surface in which only a specific step direction appears can be formed. The method of applying a control potential to the metal surface holding the adsorbed species to perform electrolytic etching or electrolytic deposition enables processing at room temperature. Therefore, unlike the method such as annealing which is usually adopted for flattening the metal surface, the metal surface is effectively flattened without giving a heat history to the base metal and without causing diffusion of impurities. In addition, the equipment does not require an atmosphere control chamber or the like, and relatively simple processing can be performed.

[0018]

【Example】

Example 1 Sulfur was strongly adsorbed by bringing a mixed gas of hydrogen and hydrogen sulfide into contact with a nickel single crystal (100) surface mirror-finished by mechanical polishing. The nickel single crystal (100) plane was immersed in a 0.05 M aqueous solution of sodium sulfate having a pH of 3.0, and the cyclic voltammogram was measured. The curve shown in FIG. 2 was obtained. Therefore, the potential was adjusted to a range of -0.6 to -0.3 V on the basis of the saturated calomel electrode, and the nickel single crystal (100) surface was electrolytically etched while observing the metal surface by STM. As can be seen from the STM image of FIG. 3 showing the electrolytically etched nickel single crystal (100) plane, an atomic level flat nickel surface having a wide terrace with a width of 100 nm or more could be exposed. When the terrace portion was further enlarged and observed by STM, as shown in the STM image in FIG. 4, sulfur was adsorbed on the nickel surface even during electrolytic etching. Further, it was found that the step directions in the electrolytic etching process were all parallel to the atomic row of sulfur. Instead of contact with hydrogen-hydrogen sulfide mixed gas, nickel single crystal (10
By dipping the 0) plane, sulfur was strongly adsorbed on the nickel single crystal (100) plane. Also in this case, a flat surface at the atomic level similar to that shown in FIGS. 3 and 4 was obtained by electrolytic etching.

Comparative Example 1: Nickel single crystal (100) under the same conditions as in Example 1 except that no adsorbed species was retained
The surface was electrolytically etched. The surface obtained in this case is
As shown in the STM image of FIG. 5, the surface was not flattened at the atomic level and had a rough surface.

Example 2 A KI solution was brought into contact with a silver single crystal (100) surface mirror-finished by mechanical polishing to strongly adsorb iodine. The silver single crystal (100) plane was immersed in a 0.1 M aqueous solution of perchloric acid, and the cyclic voltammogram was measured. The curve shown in FIG. 6 was obtained. So, RHE
(Reversible hydrogen electrode in the same solution)
The potential was adjusted to a range of 0.6 V, and the silver single crystal (100) face was subjected to electrolytic etching while observing the metal face by STM.
FIG. 7 showing an electrolytically etched silver single crystal (100) plane
As can be seen from the STM image, a flat silver surface at the atomic level having a wide terrace with a width of 50 nm or more could be exposed. Further, as a result of STM observation with the terrace portion further enlarged, it was confirmed that iodine was adsorbed on the nickel surface even during electrolytic etching.

Example 3 Subsequent to the electrolytic etching of Example 2, silver ions were electrolytically deposited while maintaining the potential at 0.4 V. According to the STM observation at this time, iodine was still adsorbed on the silver single crystal (100) surface during the electrolytic deposition process. STM silver single crystal (100) plane before and after electrolytic deposition
From the results of FIG. 8 observed, it can be seen that flat terraces at the atomic level have grown due to electrolytic deposition. Further, the step directions of the deposited terraces were all parallel to the iodine atomic rows. Comparative Example 2: The silver single crystal (100) plane was subjected to electrolytic etching under the same conditions as in Example 2 except that iodine was not adsorbed.
The steps observed during the dissolution process were not linear steps as shown in the STM image of FIG. 9, and the directions of the steps were not always constant.

[0022]

As described above, in the present invention, the metal surface on which the adsorbed species is strongly adsorbed is electrolytically etched or electrolytically deposited in an electrolyte solution. The adsorbed species strongly adsorbed on the metal surface covers a specific index surface of the metal surface and remains on the exposed metal surface even if electrolytic etching or electrolytic deposition progresses, so that the surface is not dissolved or deposited. To make it inactive. Therefore, no dissolution or precipitation occurs on the terrace, and the reaction proceeds only at sites such as steps. As a result, the metal surface becomes an atomically controlled flat surface. Further, since the atomic arrangement direction of the adsorbed species is stable, the step line extends linearly, and it becomes possible to expose the surface controlled at the atomic level. Further, when anisotropy can be provided in the step direction due to the relationship between the adsorbed species and the structure of the metal surface, a surface having a high density of existence in some step directions can be formed. As described above, according to the present invention, an atomic level suitable for magnetic recording materials, sensors, catalyst materials, battery materials, electronic device materials such as wiring on printed circuit boards, etc., which are required to have higher performance and higher density. A controlled metal surface is provided.

[Brief description of the drawings]

FIG. 1 shows a model in which the structure of the adsorbed species and the structure of the underlying metal are different in each direction in two orthogonal step portions

FIG. 2 shows a nickel single crystal (10
0) Surface cyclic voltammogram

FIG. 3 shows a scanning tunneling microscope (ST) showing a structure of a nickel single crystal (100) plane which is flattened at an atomic level.
M) Photo

FIG. 4 shows a nickel single crystal (1) during an electrolytic etching process.
STM photograph showing the structure of the (00) plane

FIG. 5 is a scanning tunneling microscope (STM) photograph showing the structure of a nickel single crystal (100) plane electrolytically etched without adsorbing sulfur.

FIG. 6 is a cyclic voltammogram of a silver single crystal (100) surface on which iodine is strongly adsorbed.

FIG. 7 shows a silver single crystal (10
Scanning tunneling microscope (STM) photograph showing the structure of the 0) plane

FIG. 8 is a scanning tunneling microscope (STM) photograph showing the structure of a silver single crystal (100) plane before (a) and after (b) electrolytic deposition.

FIG. 9 is a scanning tunneling microscope (STM) photograph showing the structure of a silver single crystal (100) plane electrolytically etched without adsorbing iodine.

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────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI C25F 3/02 C25F 3/02 A G11B 5/84 G11B 5/84 A (72) Inventor Takuya Tejima Yayoi Taishiro-ku, Sendai City, Miyagi Prefecture 22-202, Machi (72) Inventor Atsushi Mizusawa 1-4-8-305, Kongozawa, Taishiro-ku, Sendai, Miyagi Prefecture (72) Inventor Kengo Aoba 106, Aoba, Aramaki, Aoba-ku, Sendai, Miyagi Prefecture

Claims (2)

[Claims] 1. A method for strongly adsorbing an adsorbed species on a metal surface, immersing the adsorbed species in an electrolyte solution using the metal surface as a working electrode, and applying a potential to the metal surface to etch the metal surface while the adsorbed species is held,
A method for producing a metal material having a surface controlled at an atomic level, wherein a metal surface is electrolytically etched in an electrolyte solution while holding an adsorption layer. 2. A method in which an adsorbed species is strongly adsorbed on a metal surface, immersed in an electrolyte solution using the metal surface as a working electrode, and a potential at which a solute metal is deposited on the metal surface while the adsorbed species is retained is applied to the metal surface. A method for producing a metal material having a surface controlled at an atomic level, wherein a solute metal is electrolytically deposited on a metal surface in an electrolyte solution while holding an adsorption layer.