Method for manufacturing a sample, and method for observing a sample

Abstract

To provide a method of preparing a novel sample with a surface that can be suitably observed using an electron microscope without having to harden a granular material with resin and grinding it.SOLUTION: A sample preparation method comprises a first treatment step of attaching a gaseous metal compound onto a surface of a granular material to form a layer of the metal compound, and a second treatment step of reacting the metal compound with a gaseous oxidizing agent to turn the layer of the metal compound into a layer of a metal oxide or metal.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a sample and a method for observing a sample.

Background Art

[0002] For example, particulate materials such as porous materials are used as carriers for various catalysts due to their unique surface structures.

[0003] For example, Patent Document 1 describes an observation sample for observing a cross section of an inorganic porous body with an electron microscope, in which a metal having a higher secondary electron emission rate than the inorganic porous body is filled in pores of the inorganic porous body, and an observation sample of the inorganic porous body having an observation surface for observation with an electron microscope, and a method for observing the same.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the method for manufacturing a sample described in Patent Document 1, since the material is hardened with resin and then polished, the surface state of the sample may change depending on the polishing conditions. Therefore, there is a need for a new method for manufacturing a sample that can observe particulate materials without hardening them with resin and polishing them.

Means for Solving the Problems

[0006] A method for producing a sample according to one aspect of the present invention includes a first processing step of forming a layer of a metal compound by depositing a gaseous metal compound onto the surface of a material, and a second processing step of forming a layer of metal oxide or metal from the layer of metal compound by reacting the metal compound with a gaseous oxidizing agent, wherein the material includes a particulate material. [Effects of the Invention]

[0007] According to the present invention, a novel sample can be produced in which particulate material is solidified with resin and its surface can be observed suitably with an electron microscope without grinding. [Brief explanation of the drawing]

[0008] [Figure 1] This figure illustrates the schematic of an atomic layer deposition (ALD) apparatus 10 for carrying out a manufacturing method according to one aspect of the present invention. [Figure 2] This figure illustrates the schematics of the surface of a porous material after performing a manufacturing method according to one aspect of the present invention, the surface of a porous material on which metal oxides have been deposited by chemical vapor deposition (CVD), and the surface of a porous material on which metal oxides have been deposited by physical vapor deposition (PVD). [Figure 3] This is a scanning transmission electron microscope (STEM) image of a sample produced from an MEA catalyst layer by a manufacturing method according to one aspect of the present invention. [Figure 4] Figure 3 is a scanning transmission electron microscope (STEM) image of the MEA catalyst layer before the sample was prepared. [Figure 5] This is a scanning transmission electron microscope (STEM) image of a sample produced from carbon powder using the ALD film formation method according to one aspect of the present invention. [Figure 6] Figure 5 shows a scanning transmission electron microscope (STEM) image of the carbon powder before the sample was prepared. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described in detail below.

[0010] <Method for producing a sample (first aspect)> A method for producing a sample according to one aspect of the present invention includes a first processing step of forming a layer of a metal compound by depositing a gaseous metal compound onto the surface of a material, and a second processing step of forming a layer of metal oxide or metal from the layer of metal compound by reacting the metal compound with a gaseous oxidizing agent, wherein the material includes a particulate material.

[0011] In this specification, when the term "sample" is used, unless otherwise specified, it means a "sample" in which a layer of metal oxide or metal is formed by a manufacturing method according to one aspect of the present invention. In this specification, "material" is included as part of the "sample" as either the "particulate material" itself or a "material" containing at least the "particulate material". For example, if the "material" is a "porous material", it may be the "porous material" itself or a "material" containing at least the "porous material". Unless otherwise specified, "porous material" means a particulate, or in other words, powdered porous material. The surface state of the "material" can be observed by electron microscopy through the layer of metal oxide or metal formed on the "sample".

[0012] 〔material〕 The sample contains particulate material as a material. When particulate material is solidified with resin and ground, its surface state is prone to change. A method for manufacturing a sample according to one aspect of the present invention can reduce or avoid such changes in surface state while providing a high contrast to the contours of the particles.

[0013] Particulate materials may have dense irregularities on their surface. A method for producing a sample according to one aspect of the present invention can provide a high contrast to the contours of the particles, and therefore may be useful in producing a sample suitable for observing dense irregularities present on the particle surface.

[0014] The fineness of the irregularities present on the surface of the particulate material can be represented, for example, by the specific surface area of the particles. The particulate material preferably has a specific surface area of 50 m 2 / g or more, more preferably 300 m 2 / g or more. Also, although not limited, from the perspective of gas diffusion into the porous interior, the particulate material may have a specific surface area of 5000 m 2 / g or less, and may have a specific surface area of 3000 m 2 / g or less. The specific surface area of the particles can be evaluated by methods known in the art.

[0015] The particulate material may be a non-porous material or a porous material as long as it is particulate. When the particulate material is a non-porous material, examples of the non-porous material include abrasives and the like. When the particulate material is a porous material, the porous material may have the above-described dense irregularities on the surface outside the pores communicating with the inside of the particles.

[0016] (Porous material) Porous materials that can be the material of the sample have been put into practical use in a wide range of fields such as electronics, structural materials, energy, and high-functional materials, and a method for manufacturing an observation sample capable of observing the surface state of the porous material is useful. Among them, when applying carbon materials to battery materials such as fuel cells, observing the state of their pores is important for evaluating the performance of the battery materials.

[0017] Therefore, there is a need for a novel method for manufacturing a sample that can observe a particulate porous material without solidifying the particulate porous material with resin and grinding it. According to one aspect of the present invention, a novel sample can be manufactured that can preferably observe the surface with an electron microscope without solidifying the particulate porous material with resin and grinding it.

[0018] A porous material refers to a porous material, and each particle of the porous material has a large number of pores formed from the surface of the material to the inside of the material. Each of the plurality of pores on the surface of the porous material may communicate with each other inside the particles of the porous material.

[0019] In the manufacturing method according to one aspect of the present invention, the average pore diameter of the pores present on the surface of the porous material can be in the range of 1 nm to 100 nm. The average pore diameter of the pores possessed by the porous material can be determined by known methods such as the physical adsorption method of inert gases such as nitrogen and argon, and the mercury intrusion method.

[0020] The porous material can have an average particle diameter of primary particles in the range of 10 nm or more and 100 nm or less. The average particle diameter can be determined by microscopy using an electron microscope, diffusion method, method using a mobility analyzer, etc., but the microscopy method is particularly preferred. The porous material may be nodular particles, and nodular particles are aggregates of a plurality of primary particles, in other words, secondary particles.

[0021] Examples of the porous material include porous particles such as carbon, silica, and zeolite, and typically can be porous particles of a carbon material. Examples of the carbon material include porous particles formed from carbon nanotubes, fullerenes, graphene, graphite, and graphite. Among them, the carbon material includes porous particles formed from graphite.

[0022] 〔Atom Layer Deposition (ALD)〕 A manufacturing method according to one aspect of the present invention is a method for producing a sample from a material containing a porous material by atomic layer deposition, and includes a step of depositing a metal compound on the surface of the porous material (first processing step) and a step of forming a layer of metal oxide by oxidizing the metal compound deposited on the surface with an oxidizing agent (second processing step). The first and second processing steps may be repeated multiple times as a series of steps, as will be described later, and the series of steps may further include a step of supplying a purge gas.

[0023] Furthermore, in one embodiment of the manufacturing method, it is more preferable to pre-treat the porous material before depositing the metal compound on the surface of the porous material by atomic layer deposition.

[0024] (Pretreatment process for porous materials) If the porous material used in the manufacturing process is obtained, for example, as aggregates of primary particles, the porous material may be pre-treated by dispersing it in an organic solvent to break down the aggregates of porous material particles to some extent. Dispersing the porous material particles in an organic solvent also has the effect of breaking down the aggregates.

[0025] The organic solvent used in the pretreatment step is not limited as long as it is an organic solvent capable of dispersing the porous material. For example, known organic solvents such as alcohols like ethanol and i-propanol, ketones like acetone and methyl ethyl ketone, esters like ethyl acetate, ethers like dibutyl ether and 1,4-dioxane, aromatic solvents like xylene, and hydrocarbon solvents like hexane and cyclohexane can be used. The dispersion method for dispersing the porous material is not particularly limited and can be, for example, dispersed using an ultrasonic dispersion device. In the pretreatment step, it is preferable to remove the organic solvent used to disperse the porous material from the porous material before performing the first treatment step by vacuum drying, heat drying, heat-vacuum drying, or natural drying.

[0026] The porous material may, for example, be subjected to the manufacturing method according to one embodiment while supported on a support. Here, the support is not limited as long as it can support the porous material, and examples include plates or petri dishes made of glass, metal, and resin, or mesh, with mesh being preferred. The mesh is preferably a mesh commonly used in electron microscopy observation, and more preferably a metal mesh such as gold, copper, nickel, molybdenum, and SUS (stainless steel). In addition, a coating may be formed on the mesh.

[0027] (ALD equipment) A method for producing a sample based on atomic layer deposition can be suitably carried out using the ALD apparatus 10 illustrated in Figure 1. The ALD apparatus 10 comprises a reaction chamber 11, a reduced pressure section 12, a precursor gas supply section 13, an oxidizing agent gas supply section 14, and a purge gas supply section 15.

[0028] A manufacturing method according to one embodiment includes a step of depositing a metal compound on the surface of a porous material (first processing step) and a step of forming a layer of metal oxide by oxidizing the metal compound deposited on the surface with an oxidizing agent (second processing step), and these first and second processing steps are preferably carried out in a reaction chamber 11 provided in the ALD apparatus 10.

[0029] The reaction chamber 11 is independently connected to the reduced pressure section 12, the precursor gas supply section 13, the oxidizer gas supply section 14, and the purge gas supply section 15. The reaction chamber 11 is also equipped with a heating section (not shown), such as an infrared heater, which allows the temperature inside the chamber to be adjusted. In one embodiment of the manufacturing method, a layer of metal oxide is formed on the surface of a porous material by performing a first processing step and a second processing step.

[0030] The depressurization unit 12 is equipped with pumps such as a turbomolecular pump and a rotary pump. This allows the depressurization unit 12 to adjust the air pressure inside the reaction chamber 11 and to discharge unreacted metal compound gases, oxidizing agent gases, or purge gases remaining inside the reaction chamber 11.

[0031] The precursor gas supply unit 13 is equipped with a mass flow controller (MFC) that controls the flow rate and temperature of the metal compound gas, which is the precursor gas, thereby enabling control of the flow rate of the metal compound gas supplied into the reaction chamber 11.

[0032] The oxidant gas supply unit 14, like the precursor gas supply unit 13, is equipped with a mass flow controller (MFC), which allows control of the flow rate of the oxidant gas supplied into the reaction chamber 11.

[0033] The purge gas supply unit 15 supplies purge gas into the reaction chamber 11 and can control the flow rate of the purge gas.

[0034] In addition, it is preferable that the ALD apparatus 10 includes a control unit (not shown) and controls the reaction chamber 11, the reduced pressure unit 12, the precursor gas supply unit 13, the oxidizer gas supply unit 14, and the purge gas supply unit 15, respectively, so that a series of processes are repeated continuously.

[0035] [A series of steps] In one embodiment of the manufacturing method, the first processing step and the second processing step are included as a series of steps, and it is preferable to repeat this series of steps multiple times in the reaction chamber 11. This makes it possible to suitably adjust the thickness of the metal oxide layer deposited on the surface of the porous material.

[0036] Furthermore, it is more preferable that the manufacturing method according to one embodiment includes a step of purging unreacted precursor gas from the reaction chamber 11 after the first processing step and before the second processing step (first purging step), and a step of purging unreacted oxidizing agent gas from the reaction chamber 11 after the second processing step and before the subsequent first processing step (second purging step). This prevents the accumulation of unreacted material on the surface of the porous material and allows for the formation of a more homogeneous layer of metal oxide on the surface of the porous material.

[0037] In other words, from the viewpoint of the thickness of the metal oxide layer and the homogeneity of the layer, it is preferable that the manufacturing method according to one embodiment includes a first processing step, a first purging step, a second processing step, and a second purging step as a series of steps in the reaction chamber 11, and that this series of steps is repeated multiple times.

[0038] When the series of steps are carried out in the reaction chamber 11, the temperature inside the reaction chamber 11 is preferably maintained within the range of 20°C to 200°C, and more preferably within the range of 80°C to 150°C, in order to allow the metal compound to react suitably with the oxidizing agent. At this time, the atmospheric pressure inside the reaction chamber 11 is preferably maintained within the range of 200 mPa to 300 mPa.

[0039] Furthermore, it is preferable to repeat the series of steps 10 to 30 times in order to form a layer of metal oxide or metal of sufficient thickness.

[0040] (First processing step) The first processing step involves depositing a metal compound onto the surface of the porous material, thereby coating the surface of the porous material with the metal compound. The first processing step can be performed by placing the porous material S on the support mesh 20 and then placing the mesh 20 in the reaction chamber 11 (Figure 1). Prior to performing the first processing step for the first time, the air in the reaction chamber 11 may be purged with a purge gas after the mesh 20 has been placed in the reaction chamber 11.

[0041] The metal compound used in the first processing step is a precursor of a metal oxide and is supplied in a vaporized state from the precursor gas supply unit 13 into the reaction chamber 11. The precursor metal compound can be any metal compound that can be vaporized (gasified) under a heated or reduced-pressure heated environment and that produces a metal oxide when reacted with an oxidizing agent. For example, it may contain metals such as hafnium (Hf), aluminum (Al), silicon (Si), zirconium (Zr), and titanium (Ti), and the metal may be a metal compound having a functional group selected from the group consisting of alkyl groups having 1 to 5 carbon atoms, alkoxy groups having 1 to 11 carbon atoms, halogens such as chlorine and bromine, and hydrogen.

[0042] Specific examples of these metal compounds include hafnium compounds such as tetrakishafnium, aluminum compounds such as diethylaluminum ethoxide, tris(ethylmethylamide)aluminum, aluminum sec-butoxide, aluminum tribromide, aluminum trichloride, triethylaluminum, triisobutylaluminum, trimethylaluminum (TMA), and tris(diethylamide)aluminum, silicon compounds such as tetramethoxysilane and SiH4, and titanium compounds such as tetraethoxytitanium. Among these, trimethylaluminum (TMA) is a more preferred metal compound because it can be suitably gasified in the reaction chamber 11 and reacts rapidly with the oxidizing agent. These metal compounds may be supplied into the reaction chamber 11 together with an inert gas such as nitrogen, for example.

[0043] It should be noted that the above-mentioned metal compounds may form metals rather than metal oxides, depending on their type and manufacturing conditions. Therefore, the "layer of metal oxide" described below can be interpreted as a "layer of metal," but for convenience, unless otherwise specified, the present invention will be described using only the "layer of metal oxide."

[0044] In the first processing step, when the precursor gas, a metal compound gas, is supplied to the reaction chamber 11, the OH groups present on the surface of the porous material react with the metal compound. The hydrogen atom of the OH group combines with one of the functional groups of the metal compound, producing by-products, while the oxygen atom derived from the OH group combines with the metal atom. At this time, the functional groups derived from the raw material metal compound are not completely removed, and the metal compound is chemically bonded to the surface of the porous material in a partially oxidized state. The by-products vary depending on the type of metal compound, but may include, for example, alkanes such as methane and ethane, alcohols such as ethanol, halogens, and hydrogen gas.

[0045] The amount of metal compound gas supplied in one first processing step can be appropriately adjusted according to the type and amount of porous material used in the manufacturing method, but it is preferably within the range of 0.5 to 1.0 SCCM. This allows sufficient amount of metal compound to be supplied into the reaction chamber 11 to consume the hydroxyl groups present on the surface of the porous material through the reaction. Furthermore, it is preferable to perform one first processing step for 1 to 5 seconds. This allows sufficient supply of metal compound to the surface of the porous material.

[0046] (First purging process) A manufacturing method according to one embodiment more preferably includes a step (first purging step) of purging unreacted metal compound gas as unreacted material from the reaction chamber 11 after the first processing step and before the second step. The first purging step can be performed by supplying purge gas from a purge gas supply unit 15 to the reaction chamber 11 and purging the purge gas from a reduced pressure unit 12. This makes it possible to discharge unreacted metal compound gas supplied into the reaction chamber 11 in the first processing step, as well as by-products generated by the reaction, to the outside of the reaction chamber 11. This effectively prevents oxide gas supplied in the subsequent second processing step from reacting with unreacted metal compound gas remaining in the reaction chamber 11 and depositing on the surface of the porous material.

[0047] Examples of purge gases include nitrogen, as well as noble gases such as argon and helium.

[0048] Furthermore, the amount of purge gas supplied in one first purge step is preferably within the range of 90 to 100 SCCM, and the process is preferably carried out for 5 to 50 seconds.

[0049] (Second processing step) In one embodiment of the manufacturing method, an oxidizing agent gas is supplied into the reaction chamber 11 from an oxidizing agent gas supply unit 14, and the metal compound chemically bonded to the surface of the porous material is reacted with the oxidizing agent gas. This forms a layer of metal oxide on the surface of the porous material.

[0050] The oxidizing gas supplied into the reaction chamber 11 in the second processing step is typically at least one selected from the group consisting of water vapor, ozone, and oxygen plasma. These oxidizing gases may also be supplied into the reaction chamber 11 together with an inert gas, such as nitrogen.

[0051] The amount of oxidizing agent gas supplied in one second processing step can be appropriately adjusted according to the type and amount of porous material used in the manufacturing method, but it is preferably within the range of 0.5 to 1.0 SCCM. This allows sufficient amount of metal compound to be supplied into the reaction chamber 11 to consume the hydroxyl groups present on the surface of the porous material through the reaction. Furthermore, it is preferable to perform one first processing step for 1 to 5 seconds. This allows sufficient supply of oxidizing agent gas to the surface of the porous material.

[0052] In the second processing step, when the oxidizing gas is supplied to the reaction chamber 11, it reacts with the metal compound deposited on the surface of the porous material. As a result, the functional groups of the metal compound are replaced with OH groups, and a layer of metal oxide is formed. At this time, the same by-products as those produced in the first processing step are generated.

[0053] (Second purging process) After the second processing step and before the subsequent first processing step, it is preferable to purge the oxidizing agent gas and by-products remaining in the reaction chamber 11 with an inert gas. The supply conditions for the purge gas into the reaction chamber 11 in the second purging step are the same as those for the purge gas supply in the first purging step, so no explanation is provided.

[0054] In addition, in the manufacturing method according to one embodiment, it is preferable that the series of steps be completed with the second purging step as the final step.

[0055] [Sample (First Embodiment)] A sample produced by a manufacturing method according to one aspect of the present invention is a sample in which a layer selected from a layer containing metal oxides such as HfO2, Al2O3, SiO2, ZrO2, and TiO2, and a layer containing metals such as Ti and Si, covers the surface of a porous material.

[0056] Here, the thickness of the metal oxide layer formed on the sample is preferably in the range of 0.5 to 2 nm. This allows the sample to be used for clear observation of its surface state using an electron microscope.

[0057] As described above, a sample produced by the manufacturing method according to one embodiment can be suitably used, for example, as an observation sample.

[0058] <Observation Method (First Embodiment)> Observation samples produced by the manufacturing method according to one embodiment can be observed in detail using an electron microscope to determine their surface structure. The electron microscope used in the observation method according to one embodiment is preferably a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), with a scanning transmission electron microscope (STEM) being more preferable. The scanning transmission electron microscope is most preferably a high-angle scattering dark-field scanning transmission electron microscope (HAADF-STEM) from the viewpoint that the type of atom can be identified based on contrast.

[0059] A transmission electron microscope irradiates a sample with an electron beam and forms an image of the electron beam that has passed through the sample onto a fluorescent screen using a magnetic lens. The contrast of the image can be obtained through diffraction contrast or absorption contrast, which utilizes the fact that the scattering angle of the electron beam differs depending on the density and crystal orientation of the material, or through phase contrast, which is obtained by interfering electron beams whose phase has been changed by the internal potential in the sample.

[0060] Regarding this, porous materials, particularly carbon materials such as graphite, are composed of carbon atoms, which presents a problem in that it is difficult to confirm the contrast of the image produced by electron beam irradiation when observing them with an electron microscope, for example. Furthermore, the contrast of the image of graphite changes depending on the orientation of the crystal structure when irradiated with an electron beam. More specifically, when observing graphite with an electron microscope, areas with low contrast due to its carbon composition and areas with high contrast due to its crystal structure are mixed together. Due to this problem of contrast generation, it is not easy to observe the surface state and the internal structure of the pores in carbon materials such as graphite using an electron microscope. However, according to one embodiment of the observation method, by using a sample in which a metal oxide layer is suitably formed on the surface of a porous material such as a carbon material, it is possible to accurately observe the surface state while suppressing the generation of image contrast originating from the crystal structure of the porous material.

[0061] For observation of samples using scanning transmission electron microscopes (STEM) and transmission electron microscopes (TEM), the acceleration voltage is preferably in the range of 30 to 300 kV. This allows for clear imaging of the surface condition of porous materials with an extremely high resolution of 0.1 nm or less.

[0062] <Method for producing a sample and method for observing it (second aspect)> One aspect of the present invention (the first aspect) is a method for producing a sample in which a layer of metal oxide coats the surface of a particulate material, preferably a method in which a layer of metal oxide coats the surface of a porous material, but the present invention is not limited to the first aspect. Another aspect (the second aspect) is a method for producing a sample in which a sample is produced from a material comprising a particulate material and a resin. In the method for producing a sample according to the second aspect, the particulate material contained in the resin may be a non-porous material or a porous material, but it is preferably a porous material.

[0063] [Materials used in the manufacturing process] The particulate material used in the manufacturing method according to this embodiment is preferably a porous material, and is typically a catalyst layer containing the carbon material described in the manufacturing method according to the first embodiment as a support for the metal catalyst. More specifically, the material used in the manufacturing method according to this embodiment is a composition that forms a catalyst layer provided on both sides of a polymer film in a film / electrode assembly (MEA).

[0064] In solid fuel cells, a membrane / electrode assembly (MEA) is used as a membrane / electrode assembly comprising a polymer membrane and a catalyst layer, with catalyst layers (also called gas diffusion layers) provided on both sides of the polymer membrane. One of the catalyst layers functions as the cathode, and the other as the anode.

[0065] The composition constituting the catalyst layer includes a carbon material as a porous material, and further includes at least one resin selected from the group consisting of cellulose-based resins and ionomers as a resin. The composition forming the catalyst layer may also further include a noble metal-based catalyst.

[0066] Ionomers are resins used as materials for proton-conducting polymer films, and in film / electrode assemblies, ionomers similar to those used in polymer films are employed as binders to bond the catalyst layer containing porous material to the polymer film.

[0067] More specifically, ionomers include, for example, ion-exchange polymers having sulfonic acid groups, and among these, fluorinated polymers having sulfonic acid groups, such as perfluorosulfonic acid polymers, which are materials with excellent proton conductivity, strength, and chemical stability. Specific examples of fluorinated polymers having sulfonic acid groups include Nafion®, Flemion®, and Aciplex®. Specific examples of non-fluorinated polymers include, for example, polystyrene, polyarylene ethers such as polyetheretherketones, aromatic polyimides, polyphosphozenes, and aromatic polymers selected from polybenzoimidazole, in which the aromatic ring has been sulfonated. These may be composed as copolymers with olefins.

[0068] Furthermore, examples of cellulose-based resins include cross-linked sulfoethyl cellulose, which is obtained by sulfoethylating cellulose.

[0069] In the catalyst layer of the anode, metal particles containing platinum group metals (PGMs), such as platinum catalysts, ruthenium catalysts, and ruthenium-platinum alloy catalysts, are preferably used, while in the catalyst layer on the cathode side, metal particles such as platinum catalysts are preferably used.

[0070] Furthermore, the catalyst layer, which is the material, can be taken from the film / electrode assembly, and a portion of the film / electrode assembly may be cut out and a layer of metal oxide or metal may be formed by the manufacturing method according to one embodiment. In other words, the film / electrode assembly equipped with a polymer film itself can also be the material for the sample.

[0071] (Manufacturing method) The manufacturing method other than the materials is the same as the manufacturing method for the first embodiment, so its explanation is omitted.

[0072] [Observation Method] In the observation method according to this embodiment, the sample is observed using a scanning transmission electron microscope (STEM), similar to the observation method according to the first embodiment. Here, the acceleration voltage is preferably in the range of 30 to 300 kV. This makes it possible to clearly image the surface state of particulate non-porous materials or porous materials with an extremely high resolution of 0.1 nm or less, without being affected by the internal crystal structure, similar to the observation method according to the first embodiment. Furthermore, when observing a sample manufactured by the manufacturing method according to this embodiment at an acceleration voltage of 30 to 300 kV, the ionomer can be prevented from being damaged by the electron beam by the metal oxide layer or metal layer.

[0073] In particular, when observing a sample using a high-angle scattering dark-field scanning transmission electron microscope (HAADF-STEM), a narrowly focused electron beam is scanned across the sample surface, and the transmitted electrons are detected. This allows for a contrast in the sample image that is proportional to the atomic weight. This is expected to enable elemental mapping of the catalyst layer composition.

[0074] In addition, in one aspect of the observation method, elemental analysis can be performed by combining scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), etc.

[0075] <Method for manufacturing and observing a sample according to yet another embodiment (third embodiment)> One aspect of the present invention relates to a method for observing a sample, which involves a sample being manufactured by coating the surface of a particulate non-porous material or a porous material with a layer of metal oxide or a layer of metal. However, the present invention is not limited to the first or second aspect.

[0076] In a sample manufacturing method according to one aspect of the present invention, as described above, a layer of metal oxide (or metal) is formed on the surface of the material by atomic layer deposition (ALD). That is, in a sample manufacturing method according to one aspect, a metal compound gas is supplied to the surface of the sample and chemically bonded, then the metal compound gas is removed and an oxidizing agent gas is supplied to the surface of the porous material. This prevents the metal compound gas and the oxidizing agent gas from reacting with each other in the air inside the reaction chamber. Furthermore, since the metal compound gas and the oxidizing agent gas are supplied to the surface of the sample in gaseous form, it is expected that the metal compound gas and the oxidizing agent gas can be suitably supplied not only to the outer surface of the sample but also to the inner surface of the pores present on the outer surface of the sample.

[0077] Therefore, as shown in Figure 2, in the sample manufacturing method according to one aspect of the present invention (ALD method), it is expected that a uniform layer can be formed not only on the external surface of the sample but also on the internal surface of the pores present in the sample. In contrast, for example, as shown in Figure 2, in chemical vapor deposition (CVD method), a metal compound gas and an oxidizing agent gas are reacted in the reaction chamber, making it difficult to introduce metal oxide particles into the pores of the sample. Similarly, in physical vapor deposition (PVD method), it is not easy to introduce charged metal particles into the internal surface of the pores present on the surface of the sample.

[0078] In the manufacturing method according to one aspect of the present invention, it is expected that a sample produced will be able to form a uniform layer extending to the inner surface of the pores present in the sample. Therefore, by combining electron microscopy observation with X-ray analysis and using a dynamic contour model, it is expected that the structure in the sample tomography can be extracted as a contour in the electron microscope tomographic image, thereby enabling sample observation by three-dimensional mapping.

[0079] Therefore, according to one aspect of the present invention, it is expected that the structure of the internal surface of pores within the sample, as well as the external surface of the sample, can be visualized in three dimensions without grinding the sample.

[0080] 〔summary〕 A method for producing a sample according to one aspect of the present invention includes a first processing step of forming a layer of a metal compound by depositing a gaseous metal compound onto the surface of a material, and a second processing step of forming a layer of metal oxide or metal from the layer of metal compound by reacting the metal compound with a gaseous oxidizing agent, wherein the material includes a particulate material.

[0081] In one aspect of the present invention, a method for producing a sample preferably uses a particulate porous material.

[0082] In a method for producing a sample according to one aspect of the present invention, it is more preferable that the particulate material is a carbon material.

[0083] In one aspect of the present invention, the method for producing a sample is more preferably characterized in that the carbon material is graphite.

[0084] A method for producing a sample according to one aspect of the present invention may involve the material comprising the particulate material and a resin, wherein a layer of the metal oxide or the metal may be formed on the surface of the material.

[0085] In one aspect of the present invention, the method for producing a sample may also involve using an ionomer as the resin.

[0086] In one aspect of the present invention, the method for producing a sample is more preferably such that the metal contained in the metal compound is one metal selected from the group consisting of hafnium, zirconium, aluminum, silicon, and titanium.

[0087] In a method for producing a sample according to one aspect of the present invention, it is more preferable that the metal compound is trimethylaluminum.

[0088] In one aspect of the present invention, the method for producing a sample is more preferably characterized in that the gaseous oxidizing agent is one or more selected from the group consisting of water vapor, ozone, and oxygen plasma.

[0089] In one aspect of the present invention, the method for producing a sample may involve reacting the metal compound with the oxidizing agent at a temperature in the range of 20°C to 200°C in the first and second processing steps.

[0090] In one aspect of the present invention, the method for producing a sample is more preferably performed by repeating the first processing step and the second processing step multiple times as a series of steps.

[0091] In one aspect of the present invention, a method for producing a sample more preferably further includes a purging step in which the series of steps are purged with an inert gas between the first processing step and the second processing step, and between the second processing step and the first processing step, for purging unreacted gaseous metal compounds and unreacted gaseous oxidizing agents.

[0092] A method for observing a sample according to one aspect of the present invention comprises a manufacturing step of producing a sample by performing a sample manufacturing method according to one aspect of the present invention, and an observation step of observing the sample with an electron microscope.

[0093] In one aspect of the present invention, the method for observing a sample is more preferably performed using a scanning transmission electron microscope.

[0094] In one aspect of the present invention, a method for observing a sample may be used to observe the sample using an electron microscope with an accelerating voltage in the range of 30 to 300 kV.

[0095] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0096] A sample for Example 1 was prepared by forming a metal oxide layer on a catalyst layer taken from MEA, and its surface state was observed using a scanning transmission electron microscope.

[0097] (Preparation of observation samples) MEA (Membrane Electrode Assembly; Product Name: Hydrogen) Approximately 5 mg of the catalyst layer from an Air MEA-5 layer (10 × 10 cm, manufactured by Mauvik Co., Ltd.) was scraped off using a spatula and mixed with approximately 5 mL of ethanol in a sample bottle to obtain a mixture. Next, the obtained mixture was subjected to ultrasonic dispersion for approximately 1 minute to obtain an ethanol dispersion of the catalyst layer.

[0098] Next, the ethanol dispersion of the catalyst layer was dropped multiple times onto a 150-mesh STEM electron microscope (3 mm in diameter, copper mesh, manufactured by Oken Shoji Co., Ltd.) using a pipette, and the catalyst layer on the mesh was allowed to air dry.

[0099] (ALD treatment) The sample was placed on a mesh and fixed inside the reaction chamber of an ALD instrument, AT-400 (manufactured by Anric Technologies), and then subjected to ALD treatment. The conditions for the ALD treatment were as follows: Precursor gas: Trimethylaluminum (TMA) Oxidizing gas: H2O Purge gas: N2 Reaction room temperature: 150℃ A series of processes consisting of a precursor gas treatment process, a precursor gas purging process, a steam gas treatment process, and a steam gas purging process was performed consecutively for one cycle, and this cycle was repeated 20 times, resulting in a total treatment time of 30 minutes. Precursor gas treatment: 0.5 seconds, TMA flow rate 0.75 SCCM Purge gas treatment: 8 seconds, purge gas flow rate: 96 SCCM Steam treatment: 0.5 seconds, steam flow rate 0.75 SCCM Purge gas treatment: 10 seconds, purge gas flow rate: 96 SCCM This series of processes was carried out in a reaction chamber at a temperature of 150°C and a vacuum of 225 mPa, repeated for 20 cycles, with a total reaction time of approximately 30 minutes. The ALD treatment yielded observation samples coated with a metal film of approximately 2 nm.

[0100] (HAADF-STEM observation) STEM observation of the sample from Example 1 was performed using a scanning transmission electron microscope JEM-ARM200F (manufactured by JEOL Ltd.). The acceleration voltage for STEM observation was set to 200kV, and the observation magnification was set to 1,000,000x. The sample was photographed. Figure 3 shows a STEM image of the catalyst layer treated with ALD under these conditions. Figure 4 shows a STEM image of the catalyst layer before treatment.

[0101] In Figure 3, the surface structure of the particulate porous material in the catalyst layer was observed in detail because the surface was coated with a metal oxide film. Furthermore, because the ionomer was protected by the metal oxide film, it could be observed together with the porous material, as shown by the dashed line in Figure 3.

[0102] In Figure 4, the detailed surface structure of the particulate porous material in the catalyst layer is not observed, and as shown by the dashed line in Figure 4, the ionomer that should be present between the porous materials is not observed. This is thought to be because the ionomer was destroyed by the electron beam.

[0103] A sample for observation in Example 2 was prepared by forming a layer of metal oxide on a carbon material, and its surface state was observed using a scanning transmission electron microscope.

[0104] 300m as material 2 Except for using carbon powder with a specific surface area of ​​1 / g, the preparation of the observation sample, ALD treatment, and HAADF-STEM observation were performed in the same manner as in Example 1. STEM images of the ALD-treated carbon powder are shown in Figure 5. STEM images of the carbon powder before treatment are shown in Figure 6.

[0105] As shown in Figures 5 and 6, the ALD-treated observation sample showed a greater contrast in the outline of the carbon material compared to the observation sample that had not undergone ALD treatment, allowing for clear observation of the surface condition. Because the surface condition can be observed so clearly, the sample manufacturing method in one aspect of the present invention is expected to be useful for samples used in methods for observing the three-dimensional structure of a sample, such as 3D-STEM.

Claims

1. A first processing step involves forming a layer of the metal compound by depositing a gaseous metal compound onto the surface of the material, The process includes a second processing step of reacting the metal compound with a gaseous oxidizing agent to form a layer of metal oxide from the layer of the metal compound, The aforementioned material has a specific surface area of ​​50 m². ２ A manufacturing process for producing a sample, which includes particulate material of / g or more, and a method for producing a sample, and A method for observing a sample, comprising the step of observing the fine irregularities present on the surface of the particulate material by observing the sample with an electron microscope.

2. The method for observing a sample according to claim 1, wherein the particulate material is a particulate porous material.

3. The method for observing a sample according to claim 1 or 2, wherein the material further comprises a resin, and a layer of the metal oxide is formed on the surface of the material.

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