JP4838201B2 - Method for producing anodized porous alumina - Google Patents

Description

The present invention relates to a process for the preparation of anodic porous alumina.

  It is known that an anodized porous alumina layer can be formed on the surface by anodizing aluminum. This anodized porous alumina is formed with uniform and fine pores oriented perpendicular to the film surface. By filling the pores with other substances such as metals, semiconductors and organic matter, It is possible to produce composites having a regular pore structure on a meter scale, and application to electric / electronic, optical, or magnetic devices is expected.

  This is because, in anodized porous alumina, a pore structure having a high aspect ratio (pore length / pore diameter ratio) that is oriented perpendicularly to the film surface can be easily obtained. It is because the composite which consists of an alumina and a high aspect ratio filling substance is easily obtained by filling. As one of typical applications of these composites, there is a perpendicular magnetic recording medium manufactured by filling a ferromagnetic material (ferromagnetic metal) in anodized porous alumina pores. In a perpendicular magnetic recording medium, it is necessary to have perpendicular anisotropy in the medium plane, but anodized porous alumina pores having a structure in which each pore is oriented perpendicular to the film surface is filled with a ferromagnetic metal. Thus, a recording medium having perpendicular magnetization anisotropy can be easily obtained.

  Conventionally, substances are filled into anodized porous alumina by an electrochemical method, a sol-gel method in which an oxide sol solution is filled and then solidified, or a chemical precipitation method based on oxide precipitation induced by a change in chemical equilibrium. Are known.

On the other hand, based on a so-called vacuum deposition method in which a desired substance is vaporized and then deposited in the pores, a method of filling the substance in the pores is also known. According to this method, although it is possible to easily fill the pores without depending on the chemical reaction, since the directity of the pores on the surface of the anode porous alumina is low, a sufficiently high aspect ratio ( Filling with a pore length / pore diameter ratio) was difficult. That is, in the porous alumina produced by anodic oxidation, the oxide film layer formed at the initial stage of anodic oxidation is usually formed because the solubility is lower than the oxide layer formed thereafter. Since the pore diameter at the opening of the pore is smaller than the pore diameter at the back of the pore and the inlet of the pore is blocked, it becomes difficult to fill the vapor deposition substance to the back. Yes. In addition, the pores themselves may be bent from the opening to the back, which also makes it difficult to fill the vapor deposition material with a high aspect ratio.
Masuda et al., Abstracts of Autumn Meeting of the Electrochemical Society of Japan, 2E28 (2001)

An object of the present invention is to provide a method for producing an anodized porous alumina. For example, when filling other materials into the pores of an anodized porous alumina by a vacuum deposition method, a high aspect ratio filling structure can be easily provided. Another object of the present invention is to provide a method for producing an anodized porous alumina suitable for use in producing an anodized porous alumina composite that can be achieved at low cost.

In order to solve the above problems, a method for producing an anodized porous alumina according to the present invention is a method for producing an anodized porous alumina,
(1) A process of anodizing an aluminum material ,
(2) A step of expanding the pore opening of the anodized porous alumina formed in the step by an etching process ,
(3) performing anodization again and forming pores extending from the bottom of the pores formed so far ;
(4) Furthermore, the process of performing the etching process with respect to the pore formed so far ,
The steps (3) and (4) are repeated a plurality of times,
The method is characterized in that the opening of the pore has a trumpet shape and the cross-sectional shape of the pore has a step shape .
That is, first, the portion of the pore opening portion of the pore structure of the anodized porous alumina that was formed so as to close the opening portion is selectively dissolved and removed by an etching process to secure an opening portion having a desired pore diameter. To do. Thereby, for example, when filling other materials into the pores by vacuum deposition, the deposited material can easily reach the inner part of the pores, thereby easily having a high aspect ratio filling structure. A complex is obtained.

In the present invention, in particular, by performing anodization again after the etching process, a pore extending further from the bottom of the pore that was initially formed is formed. Etching is performed. In addition, by repeating this anodization and etching treatment a plurality of times, dissolution at the pore openings proceeds more and the desired pore opening is expanded more reliably, and the pore opening side Since the cross-sectional shape that has been increased in diameter becomes a stepped pore shape, for example, in the case of vacuum vapor deposition, it is more easily filled deep into the pore. Furthermore, in the present invention, as illustrated in FIG. 5 to be described later, the pore opening portion that is opened in a trumpet shape is formed more actively by utilizing the diameter expanding action of the pore opening portion by the etching process, and the substance is more Easy to fill. With such a configuration, it becomes possible to easily perform control of the filling depth (filling amount) of the substance into the pores by vacuum deposition.

  Further, in vacuum deposition, it is preferable that the deposition beam and the pores be in a parallel relationship as much as possible for sufficient filling, but this is, for example, a deposition source and a substrate in vacuum deposition. A collimator is installed between the anodized porous alumina to improve the straightness (straightness) of the atomic beam (deposition beam) from the deposition source, make the deposition beam parallel to the pore extension direction, This can be achieved by making it easier to fill the pores.

  What is necessary is just to determine the said other substance with which it fills in a pore according to the use of a composite_body | complex. For example, in the case of the perpendicular magnetic recording medium as described above, a ferromagnetic material may be used as another substance filled in the pores. Such an anodized porous alumina composite produced by using the method of the present invention can be used to constitute, in particular, an electric / electronic, optical or magnetic device.

According to the present invention, for example, as shown in FIG. 6 described later, anodized porous alumina in which a plurality of pore portions are formed by performing anodizing treatment and etching treatment, and the cross-sectional shape of the pores is stepped. An anodized porous alumina is provided .

As described above , according to the method for producing an anodized porous alumina according to the present invention, for example, when producing an anodized porous alumina composite by filling other substances in the pores, compared to the conventional method, It becomes possible to fabricate a complex in which the material is easily and densely filled in the pores of the anodized porous alumina. As a result, it is possible to fabricate a high-performance device.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 schematically shows the basic concept of anodizing, vacuum deposition, and smoothing processes when anodized porous alumina composite is produced by filling the pores with other substances using the present invention. It shows. That is, by anodizing the A Le Miniumu material 1, a layer of anodized porous alumina 3 having regular pores 2 are formed. If the two-step anodizing treatment is performed, the uniformity and regularity of the pores 2 can be improved. Another material such as nickel is deposited on the anodized porous alumina 3 by vacuum deposition. The vapor deposition material 4 is filled in the pores 2 of the anodized porous alumina 3, but is also deposited on the surface other than the pores 2, and as a result, irregularities are formed on the surface. Remove chemically and smooth the surface. By such a method, for example, the structure of the anodized porous alumina composite 5 suitable for a perpendicular magnetic recording medium or the like is completed.

  In such a basic process, as described above, in the step of forming porous alumina 3 by anodic oxidation, as shown in FIG. 2, an oxide film layer formed in the initial stage of anodic oxidation is oxidized thereafter. Since the solubility is lower than that of the physical layer, a portion 6 (oxide film portion) having a small pore diameter is formed in the opening of the pore 2 so as to close the opening. When vacuum deposition is performed in this state, as shown in FIG. 3, the vapor deposition material 4 is not uniformly filled in the pores 2 and is unevenly distributed or does not reach the inner part of the pores 2. Invite. In addition, the pores 2 themselves may be bent, which also encourages insufficient filling.

  Therefore, in the present invention, specific processing as shown in FIGS. 6 and 7 described later is performed. Prior to the description with reference to FIGS. 6 and 7 to be described later, first, the basic technical concept which is a premise in the present invention will be described. As shown in FIG. 4, the oxide film portion 6 existing at the opening of the pore 2 is removed by performing an etching process prior to the material filling based on the vacuum deposition method, thereby sufficiently expanding the diameter. The formed pore opening 7 is secured, and then the substance 4 is filled by vacuum deposition. Since the substance 4 is filled in the state where the sufficiently enlarged pore opening 7 is secured, the substance 4 is sufficiently filled in the pore 2 from the inlet to the innermost part as shown in FIG. Filled with honey. After vapor deposition, the above-described surface smoothing is performed, and the desired structure of the anodized porous alumina composite 5 is completed.

As an etching treatment in the production of the anodized porous alumina, a dry etching process such as ion milling can be used in addition to an etching solution for dissolving an anodized porous alumina represented by phosphoric acid.

Further, in the process shown in FIG. 4, only the oxide film portion 6 is mainly removed by the etching process , but in the present invention, in particular, the effect of expanding the pore opening by the etching process is more actively used. For example, as shown in FIG. 5, a pore opening 8 that is opened in a trumpet shape is formed to make it easier to fill the substance 4 . With such a configuration, it becomes possible to easily control the filling depth (filling amount) of the substance 4 into the pores 2 by vacuum deposition.

In the present invention, the pores 2 are formed as follows. As shown in FIG. 6, after securing the pore opening 7 whose diameter has been expanded by the etching process as described above, anodization is further performed, and a finer extending further from the bottom of the pore 2 formed so far. Holes 9 are formed, and these two pores 2 and 9 are further etched. Then, further pores 10 are added by further anodizing . Further, an etching process can be performed subsequently. The cross-sectional shape of each of the plurality of pores formed by such anodizing treatment and etching treatment is formed into a step-like cross-sectional shape as shown in FIG. Further, by repeating the anodic oxidation and the etching process as described above, it becomes possible to make the pores 11 close to an inverted trapezoidal shape as shown in FIG. It becomes possible.

  In addition, in order to more easily supply the material by vacuum deposition and more reliably supply deep into the pores, the straightness of the vapor deposition beam from the vapor deposition source is ensured, and the straight direction and the extension of the pores are secured. It is preferable that the current direction is parallel. For this purpose, a collimator may be used as described above.

Hereinafter, the present invention will be described based on examples.
Reference Example 1
0.3M oxalic acid was electrolyzed, and anodization was performed at 40V and 40s for 30s under the condition of 16 ° C. Thereafter, the sample was immersed in 5 wt%, 30 ° C. phosphoric acid for 10 min, and subjected to a pore diameter enlargement treatment of the pore opening. The sample was washed with water and dried, and then filled with metal (Ni) by vacuum deposition. In vacuum deposition, Ni was vacuum deposited using an electron beam melting method under the condition of a pressure of 1.3 × 10 ⁻³ Pa. The vacuum deposition rate at this time was 0.2 nm / s. After vapor-depositing Ni having a thickness of 200 nm, the sample was broken and observed with a scanning electron microscope. As a result, it was confirmed that Ni was sufficiently filled in the pores.

Example 2
Anodization and etching were performed in the same manner as in Example 1, and then 30s anodization was performed again under the same conditions. Thereafter, the sample was immersed for 10 min in 5 wt%, 30 ° C. phosphoric acid, and subjected to a pore diameter expansion treatment. Thereafter, the same anodic oxidation and pore diameter expansion treatment were again performed for two cycles. In the hole diameter enlargement process in the second cycle, the hole diameter enlargement process time was set to 15 minutes. The sample was washed with water and dried, and then filled with metal (Ni) under the same conditions as in Example 1. As a result of scanning electron microscope observation, it was confirmed that Ni was sufficiently filled in the pores.

Example 3
0.3M sulfuric acid was electrolyzed, and anodization was performed for 30 s at 25 V under the condition of 0 ° C. Thereafter, the sample was immersed for 10 min in 5 wt%, 30 ° C. phosphoric acid, and subjected to a pore diameter expansion treatment. Thereafter, the same anodic oxidation and pore diameter expansion treatment were again performed for two cycles. In the hole diameter enlargement process in the second cycle, the hole diameter enlargement process time was set to 15 minutes. After the sample was washed with water and dried, Ni was filled by vacuum deposition in the same manner as in Example 1. After Ni deposition, the sample was broken and observed with a scanning electron microscope. As a result, it was confirmed that Ni was sufficiently filled in the pores.

Reference Example 4
In the same manner as in Example 1, Co was filled into the pores of the anodized porous alumina using a vacuum deposition method. The degree of vacuum, the deposition rate, and the deposited film thickness are the same as in Example 1. As a result of observation with a scanning electron microscope, it was confirmed that the pores were sufficiently filled with Co.

Reference Example 5
In the same manner as in Example 1, Si was filled into the pores of the anodized porous alumina using a vacuum deposition method. The degree of vacuum, the deposition rate, and the deposited film thickness are the same as in Example 1. Thereafter, as a result of observation with a scanning electron microscope, it was confirmed that the pores were sufficiently filled with Si.

Reference Example 6
In the same manner as in Example 1, phthalocyanine was filled into the anodized porous alumina pores using a vacuum deposition method. A tungsten thermal evaporation source was used as the evaporation source. The degree of vacuum, the deposition rate, and the deposited film thickness are the same as in Example 1. Thereafter, as a result of observation with a scanning electron microscope, it was confirmed that the phthalocyanine was sufficiently filled in the pores.

Reference Example 7
After anodizing by the same method as in Example 1, Ni was vacuum filled to fill the pores with Ni. At this time, a collimator having high-aspect-ratio direct pores was installed between the vapor deposition source and the sample. It was confirmed that Ni could be filled into the pores by using a collimator during vapor deposition.

Reference Example 8
After anodizing by the same method as in Example 1, the surface was etched by ion milling. Ion milling was performed for 8 min at a pressure of 5 × 10 ⁻³ Pa and an acceleration voltage of 5.0 kV using argon as an etching gas. Thereafter, as a result of filling with Ni under the same conditions as in Example 1, it was confirmed that the metal could be sufficiently filled.

It is a schematic block diagram which shows the basic concept of the process in the method which concerns on this invention. It is a schematic sectional drawing which shows the pore form in the anodized porous alumina preparation stage. It is a schematic sectional drawing which shows the state in the case of performing vapor deposition with the form of FIG. It is a schematic block diagram which shows the manufacturing process of the anodized porous alumina composite containing the etching process in this invention. It is a schematic block diagram which shows another example of the etching process with respect to a pore opening part. It is a schematic block diagram which shows the example in the case of repeating the anodizing and etching process in the method which concerns on one embodiment of this invention. It is a conceptual diagram of the pore shape formed by the process of FIG.

Explanation of symbols

1 Aluminum Material 2 Pore 3 Anodized Porous Alumina 4 Vapor Deposition Material 5 Anodized Porous Alumina Composite 6 Portion with Small Pore Diameter (Oxide Film Part)
7 Expanded pore openings 8 Trumpet-shaped pore openings 9 Further extending pores 10 Further pores 11 Pores close to inverted trapezoidal shape

Claims (2)

A method for producing anodized porous alumina, comprising:
(1) A process of anodizing an aluminum material,
(2) A step of expanding the pore opening of the anodized porous alumina formed in the step by an etching process,
(3) performing anodization again and forming pores extending from the bottom of the pores formed so far;
(4) Furthermore, the process of performing the etching process with respect to the pore formed so far,
The steps (3) and (4) are repeated a plurality of times,
A method for producing anodized porous alumina, characterized in that the opening of the pore has a trumpet shape and the cross-sectional shape of the pore has a stepped shape.   The method for producing anodized porous alumina according to claim 1, wherein the final step is an anodizing step.

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