JP2958288B2 - Metallic nickel or nickel-based alloy having surface controlled at atomic level and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to metallic nickel or nickel-based alloy having a surface controlled at an atomic level and suitable as a magnetic recording material such as a magnetic recording medium and a magnetic head, a sensor, a catalyst material, a battery material and the like. And its manufacturing method.

[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. Magnetic heads used for writing to and reading from thin-film disks are also being made thinner in response to the need to increase the writing speed, and the material is mainly made of nickel from oxide materials such as ferrite. Metal material such as permalloy. In addition, to meet the needs of high recording capacity, the density of recording media has been increased,
The miniaturization of the device has been promoted, such as narrowing the head / disk, further reducing the thickness of the recording medium, and reducing the thickness of the head. 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 recent years, studies on surface reactions at the atomic level in the field of catalytic reactions and the like have revealed that the reactions vary greatly 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.

[0004]

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, since impurity elements such as sulfur usually contained in nickel diffuse and accumulate on the surface, it is extremely difficult to obtain a clean surface. 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, since the diffusion and accumulation of impurities such as S still occur at the time of annealing again, it is required 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. Normally, the surface of a metal material such as nickel is always covered with an oxide film having a thickness of about several tens angstroms in air.
To obtain a clean surface, it is first necessary to completely remove the oxide from the material surface. However, since the nickel surface has a very high reactivity to oxygen, the process of flattening the nickel surface at the atomic level uses an ultra-high vacuum to avoid contact with oxygen, and removes oxygen species from the surface. A method of processing 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. The present invention has been devised to solve such a problem, and by repeating electrolytic etching and electrolytic deposition under the condition of potential control, without requiring complicated and large-scale equipment. , Flattening the surface of metallic nickel or nickel-based alloy at atomic level, magnetic storage materials, sensors,
An object of the present invention is to provide metallic nickel or a nickel-based alloy suitable as a catalyst material, a battery material, and the like.

[0006]

In order to achieve the object, the metallic nickel or nickel-based alloy of the present invention has a flat surface free from defects on an atomic scale, in which only a specific index plane is exposed on all surface portions. It has a terrace of more than 10nm,
In addition, it has a surface having no step of 5 atoms or more in an arbitrary region. Metallic nickel or nickel-based alloy whose surface state has been flattened at the atomic level is immersed in an acidic aqueous solution using metallic nickel or nickel-based alloy as a working electrode, and 0.2% from the open circuit potential.
V With noble potential as the upper limit,-based on saturated calomel reference electrode
It is manufactured by sweeping the electrode potential of the working electrode within a range having a lower potential of 0.5 V or less as a lower limit and repeating electrolytic etching and electrolytic deposition. In processing, it is preferable to repeat electrolytic etching and electrolytic deposition while observing the surface state of metallic nickel or a nickel-based alloy with an electrochemical scanning tunneling microscope (STM).

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A metallic nickel or nickel-base alloy according to the present invention has a flat surface with no specific index plane exposed at any part of the surface and no defect on an atomic scale.
It has a surface controlled at the atomic level with a terrace of at least nm and no step of more than 5 atoms in any region. It can be said that a surface having a high density of steps acting as active sites for the reaction is difficult to act as a surface having a specific exponential plane because the factors determining the surface properties depend on the reactivity of the step. On the other hand, a surface having a step density as small as possible or a terrace having a sufficiently large terrace can be a surface utilizing characteristics of a more specific index plane. Specifically, the area of the terrace is 1
If it is 0 nm or more, the characteristics of the exposed index plane are maintained. For example, when the surface on which organic molecules are adsorbed is observed by STM, organic molecules having a regular arrangement corresponding to the exponential plane of the base are observed on a terrace having a width of 10 nm or more, whereas on a terrace narrower than that, It is difficult to obtain such a regular arrangement. Further, when the step height is 5 atoms or more, another index surface is formed on the side surface of the step, and the development of the characteristics of the specific index surface is inhibited.

The surface controlled at the atomic level is formed by using metallic nickel or a nickel-based alloy as a working electrode in an aqueous electrolyte solution and controlling the electrode potential of the working electrode to electrolytically etch the surface of the metallic nickel or nickel-based alloy. And electrolytic deposition is performed repeatedly. As the electrolyte aqueous solution, an acidic solution having a pH of less than 7.0 is preferable. pH
In a solution with a high concentration, an oxide layer is easily formed on the surface by adsorption of hydroxide ions on the metal surface before and after the treatment,
It becomes difficult to flatten the electrode surface at the atomic level.
The type of the electrolyte solution is not particularly limited as long as it is an acidic solution, and those containing any anion such as halogen, halide ion, cyanide ion, sulfate ion and nitrate ion are effectively used.

When the electrolytic deposition reaction is positively used, the aqueous electrolyte solution may contain ions of the target metal. An organic substance or the like that acts as an inhibitor in the etching reaction may be added to the electrolyte aqueous solution. Further, an electrode in which adsorbed species such as halogen and sulfur are present on the surface in advance can be used. In particular, since nickel is used as a target metal, if the treatment is performed while adsorbing species such as sulfur and iodine that strongly adsorb to the surface are retained, a flat surface at the atomic level can be obtained more effectively. Bath temperature, electrode area, counter electrode material,
Electrolysis conditions such as the amount of electricity are not particularly limited,
It is set appropriately according to the etching reaction, the electrolytic deposition reaction and the like. At the time of electrolytic etching or electrolytic deposition, the upper limit of the electrode potential is set to a potential 0.2 V more noble than the open circuit potential, and -0.
The lower limit of the electrode potential is set to a lower potential of 5 V or less. Then, the electrode potential is changed and held in this range, or the potential is repeatedly applied while sweeping the potential in this range to the working electrode.

[0010] The open circuit potential is a potential as measured without a circuit connected, while the electrode is immersed. At this potential, the anode current and the cathode current are basically balanced, and the current value is usually zero.
However, when nickel or a nickel-based alloy is immersed as an electrode, a cathode current flows due to reduction of oxygen or hydrogen dissolved in the aqueous solution. Therefore, even at the open circuit potential, a gradual anode current that balances the cathode current flows. This means that the metal surface has already been dissolved even at the open circuit potential. In the present invention, a flat surface at the atomic level is obtained by utilizing the appropriate dissolution of the electrode surface. When the surface of the electrode is maintained at an open circuit potential or a range of a potential 0.2 V higher than this potential, a slight amount is eluted by electrolytic etching. Subsequently, when the potential is shifted in a sufficiently low direction, the oxide film on the surface is reduced and removed, and the metal cation partially eluted is electrolytically deposited as a metal on the electrode surface. By repeating electrolytic etching and electrolytic deposition,
The electrode surface is flattened at the atomic level.

As a result of observing the dissolution process at the atomic level in detail using STM, it was found that the open circuit potential and the region having a potential 0.2 V higher than the open circuit potential were optimal. That is, when the electrode surface is held in this potential region, a small amount is eluted by electrolytic etching. Subsequently, when the potential is shifted in a sufficiently low direction, the oxide film on the surface is reduced and removed, and the metal cation partially eluted is electrolytically deposited as a metal on the electrode surface. The electrode surface is flattened at the atomic level by repeating the electrolytic etching and the electrolytic deposition. At this time, the open circuit potential or a potential no less than 0.2 V from this potential and a saturated calomel reference electrode-
When a process of repeatedly sweeping the potential between base potentials of 0.5 V or less is performed, the electrode surface is more effectively flattened at the atomic level. Further, a flat surface at the atomic level can be obtained by utilizing the electrolytic deposition reaction. By maintaining the electrode potential in a region sufficiently lower than the open circuit potential, an effective electrolytic deposition reaction occurs. However, in order to remove the oxide formed on the electrode surface before the treatment or in the course of dissolution, a potential of -0.5 V or less is necessary. Therefore, the lower limit of the potential is set to -0.5 V or less. .

The upper limit of the applied potential is set to a potential that is 0.2 V higher than the open circuit potential. When the electrode potential exceeds this upper limit, the dissolution rate on the electrode surface becomes extremely fast, and it becomes difficult to obtain a flat surface at the atomic level. Also, the lower limit is-based on the saturated calomel reference electrode.
At a potential higher than 0.5 V, the oxide on the electrode surface is not sufficiently reduced, and a plane flattened at the atomic level cannot be obtained. At the time of planarization, it is preferable to control the electrode potential of the working electrode while observing the polishing state using STM. Thereby, the electrode surface which is more effectively flattened at the atomic level can be obtained. Also in this case, the potential on the noble side in the potential region is further reduced from the open circuit potential to a 0.2 V noble potential, and the potential on the noble side is set to -0.5 V or less with respect to the saturated calomel reference electrode. As the STM, a commonly used STM is used as long as the electrode potential and the potential of the probe chip can be independently controlled with respect to the reference electrode. A device for applying a potential to an electrode has particular restrictions. However, as long as the electrode potential can be controlled, a device such as a potentiostat is used.

[0013]

The flattening process according to the present invention does not require annealing as in the conventional method, and therefore does not impart thermal history to the target metal nickel or nickel-based alloy. Therefore, the impurity elements contained in the metallic nickel or nickel-based alloy do not diffuse to the surface and segregate, and the mechanical properties of the material, such as a change in the crystal grain size of the material and segregation of the impurity element at the grain boundary. There is no phenomenon that affects That is, a flat surface controlled at the atomic level can be easily obtained by processing that affects only the surface.

Since the method of the present invention is a treatment in an electrolyte solution, the only required equipment is a water tank for holding a minimum amount of the solution and equipment for circulating, replenishing and discharging the solution. Equipment such as a vacuum chamber and a gas chamber necessary for controlling the atmosphere and equipment such as an exhaust system for maintaining the equipment are not required. In particular, when the present invention is applied to uses such as a magnetic recording medium, the equipment can be shared when a film is formed by a wet method such as plating. When controlling the surface morphology of metallic nickel or a nickel-based alloy by combining electrolytic etching, electrolytic deposition and oxide reduction in this way, the surface state is adjusted by controlling the potential, so that very fine surface state control is achieved. It becomes possible. Also, if the degree of processing is monitored at the atomic level using STM, it is possible to perform flattening processing to the order of nanometers or less, which was impossible with conventional techniques such as simple electrolytic etching and electrolytic deposition.

[0015]

EXAMPLE A metal nickel single crystal (111) surface was mirror-finished by mechanical polishing and immersed in a room temperature 0.05M sodium sulfate aqueous solution adjusted to pH 3.0. The open circuit potential was measured. FIG. 1 shows a cyclic voltammogram of a nickel electrode in an aqueous sodium sulfate solution measured prior to the treatment. From Figure 1, the open circuit potential (OCP) is -0.3
It turns out that it is 7V. Therefore, the upper limit of the potential control range in this embodiment is -0.17V. FIG.
It can be understood from the cyclic voltammogram that the surface of the nickel substrate slightly dissolves in the anode within the range of the processing conditions, and the reduction of the surface oxide and the electrolytic deposition of the dissolved nickel occur. After measuring the open circuit potential, the first sweep was performed by first sweeping the potential in the cathode direction as shown by the solid line in FIG. In this sweep, a gradual cathode current presumed to be caused by hydrogen generation was observed.

When the potential was turned back from the region exceeding -0.8 V and the potential was swept in the anode direction, an anode current due to the dissolution of the nickel base was observed from the region exceeding the open circuit potential. The anode current continued to flow without attenuation when the potential was further swept in the anode direction. However, this anode current is
It peaked around -0.1 V, and rapidly decreased thereafter.
This is due to an inert state in which the surface of the nickel substrate is covered with oxide, that is, passivation. Then -0.2
When the potential is turned over in the region exceeding V and swept to the cathode side, almost no current flows due to passivation.
A cathode current was observed on the cathode side from -0.3V. When the potential was further swept in the cathode direction, the cathode current increased, and one peak was formed at around 0.5V. This peak is believed to be due to the reduction of the oxide. In surface observation using STM, no oxide was observed on the electrode surface when the potential was -0.5 V or less.

Therefore, a potential was applied to nickel as follows. First, -0.85 with respect to the saturated calomel reference electrode.
V, and then the potential was swept to −0.3 V, which is slightly more noble than the open circuit potential, and then the potential was changed to −0.8 V. Note that the potential change in FIG. 1 indicates the control potential range when processing the nickel substrate, and is slightly different from the potential range of the cyclic voltammogram. The potential control was repeated while directly observing using the STM until the electrode surface was flattened at the atomic level. When the surface of the treated nickel substrate was observed by STM, an STM image of FIG. 2 indicating that the surface was flattened at an atomic level was obtained. That is, it has a flat terrace free from defects on an atomic scale of 10 nm or more, and
It was confirmed that a surface was formed in which a step having a height of 5 atoms or more was not detected in a region of m square. Furthermore,
As can be seen from the STM image of FIG. 3 in which the terrace portion was magnified and observed, atoms corresponding to the (111) plane of nickel were observed on the substrate surface, and the exposed plane was highly defined (111). Surface was confirmed.

[0018]

As described above, according to the present invention, the surface of metallic nickel or a nickel-based alloy is electrochemically processed while controlling the potential in an electrolyte solution, thereby achieving extremely high precision at the atomic level. A flattened surface can be obtained. The processed surface is used as a material for a magnetic recording medium, a magnetic recording device such as a magnetic head, a sensor, a catalyst material, a battery material, etc., whose flatness is controlled on the order of nanometers.

[Brief description of the drawings]

FIG. 1 is a graph showing a cyclic voltammogram of a nickel (111) surface in a 0.05 M aqueous solution of sodium sulfate having a pH of 3.0.

FIG. 2 is an electrochemical scanning tunneling microscopy (STM) photograph of a nickel surface processed according to the present invention showing that the nickel surface has been planarized at the atomic level.

FIG. 3 is a photograph of an electrochemical scanning tunneling microscope (STM) also observing the nickel surface with high resolution.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 5/84 G11B 5/84 A H01F 1/04 H01F 10/14 10/14 1/04 Z

Claims (3)

(57) [Claims] 1. A flat 10 nm surface free from defects on an atomic scale, wherein only a specific index plane is exposed on all surface portions.
A metal nickel or nickel-based alloy having an atomically controlled surface, having the above-mentioned terrace and having no steps of 5 atoms or more in an arbitrary region. 2. An immersion in an acidic aqueous solution using metallic nickel or a nickel-based alloy as a working electrode, with an upper limit of an additional 0.2 V noble potential from an open circuit potential, and -0.5 V or less based on a saturated calomel reference electrode. A method for producing metallic nickel or a nickel-based alloy having a surface controlled at an atomic level, characterized in that an electrode potential of a working electrode is swept within a range where the potential is a lower limit, and electrolytic etching and electrolytic deposition are repeated. 3. The method according to claim 2, wherein electrolytic etching and electrolytic deposition are repeated while observing the surface state of the metallic nickel or nickel-based alloy with an electrochemical scanning tunneling microscope.