JP2012091082A - STRUCTURE FOR RETAINING Fe FINE PARTICLE, AND CATALYST AND METHOD FOR CNT PRODUCTION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure for retaining Fe fine particles in which Fe fine particle are retained without deteriorating due to oxidation, etc., while the size of the particles is remained stable.SOLUTION: The structure is characterized in that Fe fine particles having a diameter of 5 to 20 nm exist individually and are retained on the surface layer while partially buried in the surface layer.

Description

  The present invention relates to a structure for holding nanometer-size Fe fine particles, a catalyst for producing CNTs comprising the Fe fine particles, and a method for producing CNTs using the catalyst.

  Nanosize Fe fine particles are known to be used as a catalyst for producing CNT (carbon nanotubes) as one of its uses. As is well known, CNT consists of a single layer or two or more layers of a cylindrical graphene sheet, is excellent in electron generation ability and durability, and is considered useful as an electron generation material for a field emission display of a large screen, Further, since it has high corrosion resistance, it is a substance that is expected to be used in various applications, such as being suitable for applications that require corrosion resistance such as catalyst electrode layers of fuel cells.

  As a method for producing such CNTs, an Fe layer having a predetermined thickness is formed on a predetermined surface layer, and the formed Fe layer is heat-treated to generate a large number of Fe fine particles on the surface layer. There is a method of generating CNTs using Fe fine particles as growth starting points by causing a carbon-containing gas to act.

JP 2001-303250 A

  The fine Fe particles used in such a production method must be retained in the surface layer in order to cause a carbon-containing gas to act on the fine Fe particles during the production of the CNTs. This holding will be described with reference to FIG. In the conventional Fe fine particle holding structure, as shown in FIG. 8 (a), Fe fine particles 23a and 23b having various particle diameters such as a small diameter and a large diameter are held on the surface layer 21 in a form in which the whole is exposed. ing. For this reason, when left in the air, it tends to deteriorate such as oxidation. Further, in the small-diameter Fe fine particles 23a, they disappear by reacting with the surface layer 21 due to the heating high temperature at the time of CNT generation, or move in the direction indicated by the arrow in FIG. As a result, the Fe fine particles 23b become coarse as shown in FIG. Further, since the Fe fine particles 23b are only held in an unstable state by the surface layer 21, as shown in FIG. 8 (d), the surface layer is inclined by the weight of the CNT 25 during the generation of the CNT 25. 21 is difficult to generate CNT25 in the vertical direction.

  In this way, in the conventional Fe fine particle holding structure, the state of the Fe fine particles tends to deteriorate due to oxidation or the like when placed in the air, or peels off when placed under high temperature in a vacuum or reducing gas atmosphere, It is easy to be taken in and disappeared in the lower layer, and as a result, it is difficult to use this structure for the production of CNTs.

  Under these circumstances, the Fe fine particles are not only CNT generated but also chemically stable on the surface layer 21 when they are used for other purposes, and are physically stable without being moved or disappeared. A structure that can be held in a state is required.

  Therefore, in the present invention, there is no deterioration such as oxidation even when placed under the above various environments or use, and in a stable state without causing coarsening, disappearance, movement, etc. It is an object to provide a structure capable of holding Fe fine particles.

  The structure according to the present invention is characterized in that Fe fine particles having a diameter of 5 to 20 nm are individually present on the surface layer, and a part thereof is held in a state of being buried in the surface layer.

  These Fe fine particles contain not only a simple substance of Fe but also an Fe compound.

  The Fe fine particles are preferably spherical in shape. This spherical shape is not limited to a perfect spherical shape, but includes a shape whose shape is somewhat deformed, such as an elliptical spherical shape. Further, the range of the diameter length of 5 to 20 nm is the diameter if it is a sphere, but if it is a three-dimensional shape deformed other than a sphere, at least one of the maximum and minimum lengths in various directions is the diameter. Including shapes that fall within the scope.

  The surface layer refers to the outermost surface layer, for example, the buffer layer as in the embodiment when there are a plurality of layers formed on the substrate surface, and refers to the single layer when a single layer is formed on the substrate surface, When no layer is formed on the substrate surface, it includes a portion close to the surface in the substrate.

  The material of the surface layer is not particularly limited, but is preferably Si or Al.

  According to the present invention, since the Fe fine particles are partially embedded in the surface layer, the Fe fine particles can be stably held in the surface layer, whereby the Fe fine particles can be used when used as a CNT production catalyst. The direction of the fine particles is not changed. In addition, even when exposed to the air due to alloying with Si or Al or when placed in a high temperature atmosphere, deterioration such as oxidation is suppressed and the surface of the fine particles is kept stable for a long period of time. Will be able to. Since part of the Fe fine particles are buried in the surface layer, the Fe fine particles do not move on the surface layer, and are not coalesced and coarsened with adjacent Fe fine particles. The required size and required properties of the Fe fine particles can be stably maintained. Such a case is preferable in generating CNTs having a uniform diameter when the carbon-containing gas is brought into contact with the Fe fine particles to generate CNTs on the surface of the Fe fine particles.

  In a preferred embodiment, the surface layer is a buffer layer constituting the outermost surface layer among a plurality of layers sequentially formed on the substrate surface, and the buffer layer contains Si or Al as a main component.

  In a preferred embodiment, a barrier layer is provided between the surface layer and the substrate surface, and the barrier layer is a metal oxide layer or a metal layer containing oxygen.

  According to the present invention, it is possible to provide a structure capable of holding Fe fine particles while maintaining the size of Fe fine particles stably without deterioration such as oxidation. In such a structure, when it is used as the structure of a CNT production catalyst, a CNT excellent in linearity can be easily produced with good reproducibility.

FIG. 1 is a diagram showing a cross-sectional configuration of an Fe fine particle holding structure according to an embodiment of the present invention. FIG. 2 is a diagram used for explaining a manufacturing example of the Fe fine particle holding structure of FIG. FIG. 3 is a view showing a state in which CNTs are generated in the Fe fine particle holding structure of FIG. FIG. 4A is a diagram showing a TEM photograph of the structure of FIG. FIG. 4B is a copy of the Fe fine particle holding structure shown in the TEM photograph of FIG. 4A. FIG. 5A is a view showing an SEM photograph of a CNT group generated by the structure shown in the TEM photograph of FIG. 4A. FIG. 5B is a copy of the CNT group shown in the TEM photograph of FIG. 5A. 6A is a diagram showing a TEM photograph of an arbitrary CNT in the CNT group in FIG. 5A. FIG. 6B is a copy of the CNT shown in the TEM photograph of FIG. 6A. 7 (a) and 7 (b) are views showing SEM photographs of CNTs produced by the catalyst structure of the present invention. It is a figure where it uses for description of the conventional Fe fine particle holding structure.

  Hereinafter, an Fe fine particle holding structure according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a cross-sectional configuration of the Fe fine particle holding structure. With reference to FIG. 1, the Fe fine particle holding structure 1 of the embodiment includes a substrate 3, a plurality of layers 5, 9, 11 provided on the substrate 3, and Fe fine particles 13. The substrate 3 is made of Si (silicon). The layers 5, 9, and 11 are formed on the substrate 3 in this order.

The layer 5 is a recent barrier layer on the substrate 3 and is a layer for separating the upper layers 9, 11 and the like from the substrate 3 to prevent interference therebetween. The barrier layer 5 is formed of, for example, a metal oxide such as Al ₂ O ₃ (alumina) or a metal containing oxygen. The barrier layer 5 is not necessary when a metal oxide such as Al (aluminum) or Al ₂ O ₃ is used for the substrate 3.

  The layer 9 is an Al layer containing oxygen 7.

  The layer 11 is a buffer layer mainly composed of Si or Al. The buffer layer 11 is made of Si and includes Al9a on the lower layer side. Therefore, the buffer layer 11 is mainly composed of Si or Al.

  Of the above layers 5, 9, and 11, the buffer layer 11 constitutes a surface layer.

  The Fe fine particles 13 are nm-sized Fe fine particles.

  The Fe fine particles 13 exist independently of each other, are partly buried in the buffer layer 11 that is the surface layer, and are held in the buffer layer 11 in a state where the remaining part is exposed from the surface of the buffer layer 11. Here, “independently present” means that a plurality of Fe fine particles 13 adjacent in the planar direction do not overlap each other and exist at a certain distance in the planar direction.

  In the embodiment, the Fe fine particles 13 are shown in a state in which the lower half is buried in the buffer layer 11 as a part and the upper half is exposed outside the buffer layer 11 as the remaining part. The buried form of 13 is not limited to the form shown in the drawings. The Fe fine particles 13 may be partially buried in the buffer layer 11 to the extent that they cannot move in the plane direction. For example, the buried part includes the case where the Fe fine particles 13 are buried beyond the lower half and the case where the Fe fine particles 13 are buried less than the lower half.

  Note that the term “buried” is merely an example of the form, and does not mean that it is buried in the buffer layer 11 from above.

  Fe fine particles 13 having an nm size of 5 to 20 nm in diameter are useful as a catalyst.

  Although the shape of the Fe fine particles 13 is shown as a perfect sphere in FIG. 1, the shape is not limited to such a perfect sphere, and includes a fine particle shape whose shape is deformed to a shape other than a sphere, such as an elliptic sphere or a saddle shape. .

  With reference to FIG. 2, the manufacturing process of the holding structure 1 shown in FIG. 1 will be described.

  The precursor 17 of the holding structure 1 shown in FIG. This precursor 17 is obtained by forming a barrier layer 5, an Al layer 9 containing oxygen 7, a buffer layer 11, and an Fe layer 19 in this order on a substrate 3.

  The barrier layer 5 is deposited on the substrate 3 by sputtering or ALD (atomic layer deposition). The barrier layer 5 is a layer formed of, for example, a metal oxide system or a metal containing oxygen, and the metal oxide includes, for example, alumina. However, when the substrate material itself can be used as the barrier layer such as Al or alumina for the substrate 3, the barrier layer 5 is not necessary.

The Al layer 9 is formed on the barrier layer 5 to a thickness of about 2-3 nm by sputtering or EB-PVD (electron beam physical vapor deposition). The Al layer 9 contains oxygen 7 as a nonmetallic element. The amount of oxygen 7 introduced is preferably 10 ⁻⁵ Pa to 10 ⁻² Pa in terms of pressure.

  The buffer layer 11 is formed on the Al layer 9 and is made of Si and is formed to a thickness of 5-7 nm by sputtering. The buffer layer 11 may be an alloy layer of Si and Fe. When this buffer layer 11 is used, the Fe layer 19 can be omitted.

  The Fe layer 19 is deposited to a thickness of about 2 nm as a magnetic metal layer by sputtering or EB-PVD (electron beam physical vapor deposition).

  The precursor 17 having the above configuration is thermally annealed.

  When the precursor 17 is thermally annealed, as shown in FIG. 2B, the Fe 19a once enters the buffer layer 11 from the Fe layer 19, while the Al 9a from the Al layer 9 is indicated by an arrow as indicated by an arrow. Come in.

  In this way, Fe 19a enters the buffer layer 11 from the upper layer side and Al 9a enters from the lower layer side, but Si cannot coexist with Fe 19a in the buffer layer 11, but coexists with Al 9a.

  As a result, Fe 19a in the buffer layer 11 is pushed out to the outermost surface side of the buffer layer 11 and precipitates as Fe fine particles 13.

  The Fe layer 19 in FIG. 2A is not shown in FIG. 2B, and is shown as Fe 19a in the buffer layer 11, but the Fe layer 19 partially remains on the surface of the buffer layer 11 although not shown. There is also a case. Alternatively, the Fe layer 19 may be omitted, and Si in the buffer layer 11 and Fe 19a may be alloyed as described above.

  In this case, among the Fe fine particles extruded to the outermost surface side, small-diameter Fe fine particles are not deactivated by silicidation or the like, and are not coalesced or precipitated into large-diameter Fe fine particles. As shown in (c), only a plurality of Fe fine particles 13 having a diameter equal to or larger than a certain value and a uniform diameter are deposited, and the structure 1 of the embodiment can be obtained.

  In this structure 1, as a result of the uniform diameter of the Fe fine particles 13, the activity of the Fe fine particles 13 is also uniformed. As a result, the growth rate of the CNT growing on the Fe fine particles 13 is constant, and FIG. As shown, CNTs excellent in linearity can be formed on the Fe fine particles 13.

  FIG. 3 shows a state in which CNTs 15 are generated on the Fe fine particles 13 of the Fe fine particle holding structure 1 shown in FIG. The structure 1 of the embodiment can increase the number of layers of the graphene sheet when forming the CNTs 15. As a result, the rigidity of the CNTs 15 is improved. Also from this point, the CNTs 15 having excellent linearity are easily manufactured with good reproducibility. be able to. Although detailed description of the process when using the Fe fine particles 13 on the Fe fine particle holding structure 1 as catalyst fine particles for generating CNTs 15 is omitted, the Fe fine particles 13 are brought into contact with the Fe fine particles 13 by a carbon-containing gas contact reaction. CNTs 15 are generated on the top.

  In the above, the Fe fine particle holding structure 1 of the present embodiment has been described as a catalyst structure for generating CNT 15 as an example of the application, but is not limited to the application. The Fe fine particle holding structure 1 of the embodiment has a structure in which a part of the Fe fine particle 13 is buried in the buffer layer 11 that is a surface layer and the remaining part is exposed outside the buffer layer 11, and Si or Al with respect to Fe Is alloyed at a certain ratio, so that even when exposed to air or placed in a high temperature atmosphere, deterioration such as oxidation of the Fe fine particles 13 is suppressed, and the stable state of the surface is prolonged. Will be able to keep.

  In addition, since the Fe fine particles 13 are partly buried in the buffer layer 11 independently, they do not move on the buffer layer 11 and can be combined with the adjacent Fe fine particles 13 to be coarsened. Therefore, the necessary size and necessary properties of the nanosized Fe fine particles 13 can be stably maintained.

  FIG. 4A shows a TEM photograph of the Fe fine particle holding structure of the embodiment, and FIG. 4B shows a copy of the structure shown in the SEM photograph of FIG. 4A. Referring to FIGS. 4A and 4B, the TEM photograph of FIG. 4A shows the substrate 3, the reaction layer 20, the barrier layer 5, the Al layer 9, and the buffer layer 11 in the TEM photograph of FIG. 4B. A plurality of layers 5, 9, 11 provided on the substrate 3 and Fe fine particles 13 are shown. The reaction layer 20 is a reaction layer between the substrate 3 and the barrier layer 5. As shown in the TEM photograph, the Fe fine particles 13 are shown in a state where the lower half is buried in the buffer layer 11 and the upper half is exposed outside the buffer layer 11. Several Fe fine particles 13 are shown in the TEM photograph, and it can be seen that all of them are in the diameter range of 5 to 20 nm. Further, it can be seen that the shape of each Fe fine particle 13 is substantially spherical as judged from the TEM photograph. Reference numeral 21 denotes a resin filled when photographing the Fe fine particle holding structure.

  FIG. 5A shows a TEM photograph of CNT 15 manufactured using the Fe fine particle holding structure shown in the TEM photograph of FIG. 4A, and FIG. 6A shows a TEM photograph showing an enlarged one of the CNTs 15 shown in FIG. 5A, and FIG. 6B shows a CNT15 shown in the TEM photograph of FIG. 6A. It can be seen that the CNTs 15 shown in these TEM photographs are generated on the Fe fine particles 13 with a uniform diameter and high linearity.

  FIGS. 7A and 7B show SEM photographs in which such CNTs are gathered. FIG. 7A is an SEM photograph at a magnification of 50,000 times, and FIG. 7B is an SEM photograph at a magnification of 200,000 times. As shown from these SEM photographs, the CNT 15 excellent in linearity can be manufactured using the catalyst structure of the embodiment. As an example of the SEM photograph, the substrate is placed in a vacuum chamber, heated to a high temperature of 700 ° C., acetylene gas is introduced as a carbon-containing gas, and the internal pressure of the vacuum chamber is kept constant at a predetermined pressure. It is a SEM photograph which shows that is growing.

  As described above, in the present embodiment, the Fe fine particles 13 having a diameter of 5 to 20 nm exist independently and are held in the buffer layer 11 in a state of being partially buried in the buffer layer 11. 13 is stably held in the buffer layer 11, whereby the Fe fine particles 13 are prevented from being deteriorated by oxidation or the like even when exposed to the air or placed in a high temperature atmosphere, and the surface of the Fe fine particles 13 is stabilized. It can be kept for a long time. And since the Fe fine particles 13 are partially embedded in the buffer layer 11, they do not move on the buffer layer 11, and are not coalesced and coarsened with the adjacent Fe fine particles 13. The required size and required properties can be stably maintained.

1 Fe fine particle holding structure 3 Substrate 5 Barrier layer 7 Oxygen 9 Al layer 11 Buffer layer 13 Fe fine particle 15 CNT
19 Fe layer

Claims (6)

  A structure characterized in that Fe fine particles having a diameter of 5 to 20 nm exist independently and are held on a substrate in a state of being partially buried in a surface layer.   The surface layer is a buffer layer constituting an outermost surface layer among a plurality of layers sequentially formed on the substrate surface, and the buffer layer contains Si or Al as a main component. Item 2. The structure according to Item 1.   The structure according to claim 2, further comprising a barrier layer between the surface layer and the substrate surface, wherein the barrier layer is a metal oxide layer or a metal layer containing oxygen.   A CNT produced on a Fe fine particle by bringing a carbon-containing gas into contact with the Fe fine particle, wherein the Fe fine particle is partially embedded in the surface layer in the structure according to claim 1. CNT characterized by being fine Fe particles.   A catalyst for producing CNTs comprising Fe fine particles having the structure according to any one of claims 1 to 3.   A CNT production method, comprising producing CNTs using the Fe fine particles in the structure according to claim 5 as a catalyst for CNT production.