Sample preparation method and sample observation method

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 the 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 ground, the surface state of the sample may change depending on the grinding 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 grinding them.

Means for Solving the Problems

[0006] A method for manufacturing a sample according to one aspect of the present invention includes a first treatment step of forming a layer of a metal compound by attaching a gaseous metal compound to the surface of a material, and a second treatment step of forming a metal oxide or a metal layer from the layer of the metal compound by reacting the metal compound with a gaseous oxidizing agent, and the material includes a particulate material.

Effects of the Invention

[0007] According to the present invention, there is an effect that a new sample can be manufactured which can suitably observe the surface with an electron microscope without solidifying and grinding the particulate material with a resin.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail.

[0010] <Method for manufacturing a sample (first aspect)> A method for manufacturing a sample according to an aspect of the present invention includes a first treatment step of forming a layer of a metal compound by attaching a gaseous metal compound to the surface of a material, and a second treatment step of reacting the metal compound with a gaseous oxidant to form a metal oxide or a metal layer from the layer of the metal compound, and the material includes a particulate material.

[0011] In this specification, when simply described as "sample", the "sample" means, unless otherwise specified, a "sample" in which a metal oxide or a metal layer is formed by the manufacturing method according to an aspect of the present invention. Further, in this specification, "material" is included as a part of the "sample" as 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". The "porous material" means, unless otherwise specified, a particulate, in other words, a powdery porous material. Note that the surface state of the "material" can be observed by an electron microscope through the metal oxide layer or the metal layer formed on the "sample".

[0012] 〔Material〕 The sample includes a particulate material as a material. When the particulate material is hardened with resin and ground, the surface state is likely to change. The method for manufacturing a sample according to an aspect of the present invention can impart a large contrast to the contour of the particles while reducing or avoiding such a change in the surface state.

[0013] The particulate material may have dense irregularities on its surface. The method for manufacturing a sample according to an aspect of the present invention can be useful in manufacturing a sample suitable for observing the dense irregularities present on the particle surface because it can impart a large contrast to the contour of the particles.

[0014] The fineness of the unevenness 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 limiting, 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. When the particulate material is a porous material, the porous material may have the above-described fine unevenness on the surface outside the pores communicating with the inside of the particles.

[0016] (Porous material) Porous materials that can be sample materials 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 capable of observing 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 by 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 its surface 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 the 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, a diffusion method, a method using a mobility analyzer, etc., but the microscopy method is particularly preferred. Note that 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] 〔Atomic Layer Deposition (ALD)〕 The manufacturing method according to one aspect of the present invention is a method for manufacturing 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 treatment step), and a step of forming a metal oxide layer by oxidizing the metal compound deposited on the surface with an oxidizing agent (second treatment step). As will be described later, the first treatment step and the second treatment step may be repeatedly performed a plurality of times as a series of steps, and further, the series of steps may include a step of supplying a purge gas.

[0023] Further, in the manufacturing method according to one aspect, it is more preferable to perform a pretreatment on the porous material before depositing the metal compound on the surface of the porous material by atomic layer deposition.

[0024] (Step of pretreating the porous material) When the porous material used in the manufacturing method is obtained, for example, as an aggregate of primary particles, as a pretreatment step of the porous material, the porous material may be preliminarily dispersed in an organic solvent to break up the aggregate of the porous material particles to some extent. Also, by dispersing the porous material particles in an organic solvent, the effect of resolving aggregation is achieved.

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

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

[0027] (ALD apparatus) The manufacturing method of a sample based on the atomic layer deposition method can be preferably performed by the ALD apparatus 10 illustrated in FIG. 1. The ALD apparatus 10 includes a reaction chamber 11, a decompression unit 12, a precursor gas supply unit 13, an oxidant gas supply unit 14, and a purge gas supply unit 15.

[0028] The manufacturing method according to one aspect includes a step of depositing a metal compound on the surface of the porous material (the first treatment step) and a step of forming a metal oxide layer by oxidizing the metal compound deposited on the surface with an oxidant (the second treatment step), and these first treatment step and second treatment step may be performed in the reaction chamber 11 provided in the ALD apparatus 10.

[0029] The reaction chamber 11 communicates separately with each of the decompression unit 12, the precursor gas supply unit 13, the oxidant gas supply unit 14, and the purge gas supply unit 15. Further, the reaction chamber 11 includes a heating unit (not shown) such as an infrared heater, etc., and thereby the temperature inside the chamber can be adjusted. The manufacturing method according to one aspect forms a metal oxide layer on the surface of the porous material by performing the first treatment step and the second treatment step.

[0030] The decompression unit 12 includes pumps such as a turbo molecular pump and a rotary pump, for example. Thereby, the decompression unit 12 adjusts the air pressure inside the reaction chamber 11 or discharges gases such as unreacted metal compound gas, oxidant gas, or purge gas remaining inside the reaction chamber 11 to the outside of 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, the flow rate of the metal compound gas supplied into the reaction chamber 11 can be controlled.

[0032] Similar to the precursor gas supply unit 13, the oxidant gas supply unit 14 is equipped with a mass flow controller (MFC), by which the flow rate of the oxidant gas supplied into the reaction chamber 11 can be controlled.

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

[0034] In addition, the ALD apparatus 10 is preferably equipped with a control unit (not shown) to control each of the reaction chamber 11, the pressure reduction unit 12, the precursor gas supply unit 13, the oxidant gas supply unit 14, and the purge gas supply unit 15 so as to continuously repeat a series of processes.

[0035] 〔A series of processes〕 The manufacturing method according to one aspect includes a first processing step and a second processing step as a series of processes, and it is preferable to repeat the series of processes a plurality of times in the reaction chamber 11. Thereby, the film thickness of the metal oxide layer deposited on the surface of the porous material can be suitably adjusted.

[0036] Moreover, the manufacturing method according to one aspect preferably includes a step of purging unreacted precursor gas from the reaction chamber (the first purge step) after the first processing step and before the second processing step, and a step of purging unreacted oxidant gas from the reaction chamber 11 (the second purge step) after the second processing step and before the next first processing step. Thereby, the deposition of unreacted substances on the surface of the porous material can be prevented, and a more homogeneous metal oxide layer can be formed on the surface of the porous material.

[0037] That is, from the viewpoints of the film thickness of the metal oxide layer and the homogeneity of the layer, the manufacturing method according to one aspect includes, in the reaction chamber 11, a first treatment step, a first purge step, a second treatment step, and a second purge step as a series of steps, and it is preferable to repeat this series of steps a plurality of times.

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

[0039] Also, the series of steps are preferably repeated 10 to 30 times in order to form a metal oxide layer or a metal layer having a sufficient film thickness.

[0040] (First treatment step) The first treatment step is a step of depositing a metal compound on the surface of the porous material, thereby coating the surface of the porous material with the metal compound. The first treatment step can be performed by placing the mesh 20 as a support in the reaction chamber 11 with the porous material S placed thereon (FIG. 1). Note that prior to performing the first first treatment step, after placing the mesh 20 in the reaction chamber 11, the air in the reaction chamber 11 may be purged with a purge gas.

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

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

[0043] Note that depending on the type and production conditions of the above-mentioned metal compound, it may form a metal instead of a metal oxide. Therefore, the "layer of metal oxide" described below can be interpreted by replacing it with a "layer of metal". For the sake of convenience, unless otherwise specified, the present invention will be described using only the "layer of metal oxide".

[0044] In the first treatment step, when a metal compound gas, which is a precursor gas, is supplied to the reaction chamber 11, the OH groups present on the surface of the porous material react with the metal compound. One hydrogen atom of the OH group binds to one functional group of the metal compound, generating a by-product, while the oxygen atom and the metal atom derived from the OH group bind to each other. At this time, the functional group derived from the metal compound as a raw material is 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, and can be, for example, alkanes such as methane and ethane, alcohols such as ethanol, and halogens, hydrogen gas, etc.

[0045] The supply amount of the metal compound gas in one first treatment step may be appropriately adjusted according to the type of the porous material to be used in the manufacturing method and the amount of the porous material, but is preferably a flow rate within the range of 0.5 to 1.0 SCCM. Thereby, an amount of the metal compound sufficient to sufficiently consume the hydroxyl groups present on the surface of the porous material by the reaction can be supplied into the reaction chamber 11. Also, one first treatment step is preferably performed for 1 to 5 seconds. Thereby, the metal compound can be sufficiently supplied to the surface of the porous material.

[0046] (First purge step) The manufacturing method according to one aspect more preferably includes a step (first purge step) of purging unreacted metal compound gas from the inside of the reaction chamber 11 as unreacted substances after the first treatment step and before the second step. The first purge step can be performed by supplying a purge gas from the purge gas supply unit 15 to the reaction chamber 11 and purging the purge gas from the decompression unit 12. Thereby, the unreacted substances of the metal compound gas supplied into the reaction chamber 11 in the first treatment step and the by-products generated by the reaction can be discharged outside the reaction chamber 11. Thereby, it is possible to suitably prevent the oxide gas supplied in the subsequent second treatment step from reacting with the unreacted metal compound gas remaining in the reaction chamber 11 and depositing on the surface of the porous material.

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

[0048] Also, the supply amount of the purge gas in one first purge step is preferably a flow rate within the range of 90 to 100 SCCM, and it is preferably performed for 5 to 50 seconds.

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

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

[0051] The supply amount of the oxidizing agent gas in one second treatment step may be appropriately adjusted according to the type of the porous material to be used in the manufacturing method and the amount of the porous material, but is preferably a flow rate within the range of 0.5 to 1.0 SCCM. Thereby, an amount of metal compound sufficient to sufficiently consume the hydroxyl groups present on the surface of the porous material by reaction can be supplied into the reaction chamber 11. Also, one first treatment step is preferably performed for 1 to 5 seconds. Thereby, the oxidizing agent gas can be sufficiently supplied to the surface of the porous material.

[0052] In the second treatment step, when the oxidizing agent gas is supplied to the reaction chamber 11, the metal compound deposited on the surface of the porous material reacts with the oxidizing agent gas. Thereby, the functional group of the metal compound is substituted with an OH group, and a layer of metal oxide is formed. At this time, the same by-products as those generated when the first treatment step is performed are generated.

[0053] (Second purge step) After the second processing step and prior to the subsequent first processing step, it is preferable to purge the oxidizing gas and the by-products remaining in the reaction chamber 11 with an inert gas. Since the supply conditions of the purge gas into the reaction chamber 11 in the second purge step are in accordance with the supply conditions of the purge gas in the first purge step, the description thereof is omitted.

[0054] In addition, in the manufacturing method according to one aspect, it is preferable that a series of steps end with the second purge step as the last step.

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

[0056] Here, the film thickness of the layer of metal oxide formed on the sample is preferably in the range of 0.5 to 2 nm. Thereby, it can be used as a sample whose surface state can be clearly observed by an electron microscope.

[0057] As described above, a sample manufactured by the manufacturing method according to one aspect is suitably used, for example, as an observation sample.

[0058] <Observation Method (First Aspect)> The surface structure of an observation sample manufactured by the manufacturing method according to one aspect can be observed in detail by an electron microscope. The electron microscope employed in the observation method according to one aspect is preferably a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), and more preferably a scanning transmission electron microscope (STEM). The scanning transmission electron microscope is most preferably a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) from the viewpoint that the type of atoms can be confirmed based on contrast.

[0059] In a transmission electron microscope, an electron beam is irradiated parallel to a sample, and the electron beam transmitted through the sample is imaged on a fluorescent screen using a magnetic field lens. The contrast of the image utilizes diffraction contrast or absorption contrast, which is based on the fact that the scattering angle of the electron beam varies depending on the density of the substance and the crystal orientation, and phase contrast obtained by interfering electron beams whose phases have been changed by the internal potential in the sample.

[0060] Regarding this, porous materials, particularly carbon materials including graphite, are composed of carbon atoms. For example, when observing with an electron microscope, there is a problem that it is difficult to confirm the contrast of the image generated by electron beam irradiation. Also, the contrast of the image of graphite changes depending on the orientation of the crystal structure when irradiated with an electron beam. More specifically, in electron microscope observation, graphite is observed such that there are mixed portions with low contrast due to being composed of carbon and portions with high contrast due to its crystal structure. Due to such a problem of contrast generation, it is not easy to observe the surface state and the internal structure of the pores of carbon materials including graphite with an electron microscope. However, according to the observation method according to one aspect, by using a sample in which a layer of metal oxide is preferably formed on the surface of a porous material including a carbon material, it is possible to accurately observe the surface state while suppressing the generation of contrast of the image derived from the crystal structure of the porous material.

[0061] In the observation of a sample by a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM), the acceleration voltage is preferably in the range of 30 to 300 kV. Thereby, the surface state of the porous material can be clearly photographed with an extremely high resolution of 0.1 nm or less.

[0062] <Sample manufacturing method and observation method (second aspect)> The method for manufacturing a sample according to one aspect (the first aspect) of the present invention is a method for manufacturing a sample in which a layer of metal oxide covers the surface of a particulate material, preferably a method for manufacturing a sample in which a layer of metal oxide covers the surface of a porous material, but the present invention is not limited to the first aspect. Further, the method for manufacturing a sample according to another aspect (the second aspect) manufactures a sample from a material including a particulate material and a resin. In the method for manufacturing 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 is preferably a porous material.

[0063] 〔Materials to be used in the manufacturing method〕 The particulate material contained in the material to be used in the manufacturing method according to this aspect is preferably a porous material, and is typically a catalyst layer containing the carbon material described in the manufacturing method according to the first aspect as a carrier for a metal catalyst. More specifically, the material to be used in the manufacturing method according to this aspect is a composition for forming a catalyst layer provided on both sides of a polymer membrane in a membrane / electrode assembly (MEA).

[0064] In a solid oxide fuel cell, the membrane / electrode assembly (MEA) is used as a membrane / electrode assembly including a polymer membrane and a catalyst layer, and catalyst layers (also referred to as gas diffusion layers) are provided on both sides of the polymer membrane. One of the catalyst layers functions as a cathode and the other functions as an 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 a cellulose-based resin and an ionomer as a resin. Further, the composition for forming the catalyst layer may further include a noble metal-based catalyst.

[0066] An ionomer is a resin used as a material for a proton-conductive polymer membrane. In a membrane / electrode assembly, the same ionomer as that used for the polymer membrane is adopted as a binder for joining the catalyst layer containing a porous material and the polymer membrane.

[0067] Ionomers include, more specifically, for example, ion-exchange polymers having sulfonic acid groups. Among them, materials excellent in proton conductivity, strength, and chemical stability, such as fluorine-based polymers having sulfonic acid groups like perfluorosulfonic acid polymers, can be used. Specific examples of fluorine-based polymers having sulfonic acid groups include Nafion (registered trademark), Flemion (registered trademark), and Aciplex (registered trademark). As non-fluorine-based polymers, specifically, for example, those obtained by sulfonating aromatic rings in aromatic polymers selected from polyarylene ethers such as polystyrene and polyether ether ketone, aromatic polyimides, polyphosphazenes, and polybenzimidazoles can be mentioned, and these may be configured as copolymers with olefins.

[0068] In addition, examples of cellulose-based resins include crosslinked sulfonated ethyl cellulose obtained by sulfonating ethyl cellulose.

[0069] As the noble metal-based catalyst, in the catalyst layer of the anode, for example, metal particles containing platinum group metals (PGM) such as platinum catalysts, ruthenium catalysts, and ruthenium-platinum alloy catalysts are preferably used, and in the catalyst layer on the cathode side, for example, metal particles such as platinum catalysts are preferably used.

[0070] Note that the catalyst layer as a material may be collected from the membrane / electrode assembly, and a part of the membrane / electrode assembly may be cut out to form a metal oxide layer or a metal layer by the manufacturing method according to one aspect. That is, the membrane / electrode assembly itself provided with a polymer membrane can also be a sample material.

[0071] (Manufacturing method) The manufacturing methods other than the materials are the same as those of the manufacturing method according to the first aspect, so the description thereof is omitted.

[0072] 〔Observation method〕 In the observation method according to this aspect, similar to the observation method according to the first aspect, a sample is observed with a scanning transmission electron microscope (STEM). Here, the acceleration voltage is preferably in the range of 30 to 300 kV. Thereby, similar to the observation method according to the first aspect, the state of the surface of a particulate non-porous material or a porous material can be clearly imaged with an extremely high resolution of 0.1 nm or less without being affected by the internal crystal structure. Furthermore, for a sample manufactured by the manufacturing method according to this aspect, when observing the sample at an acceleration voltage of 30 to 300 kV, damage to the ionomer by the electron beam can be prevented by the layer of metal oxide or the layer of metal.

[0073] In particular, when observing a sample with a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), by scanning a narrow electron beam on the sample surface and detecting the transmitted electrons, contrast proportional to the atomic weight can be obtained in the image of the sample. Thereby, it can be expected that elemental mapping in the composition of the catalyst layer becomes possible.

[0074] In addition, in the observation method according to one aspect, energy dispersive X-ray spectroscopy (EDS method), electron energy loss spectroscopy (EELS method), etc. can be combined with scanning transmission electron microscope observation to perform elemental analysis.

[0075] <Furthermore, a manufacturing method and an observation method of a sample according to still another aspect (third aspect)> The observation method of a sample according to one aspect of the present invention is a manufacturing method of a sample in which a layer of metal oxide or a layer of metal covers the surface of a particulate non-porous material or a porous material, but the present invention is not limited to the first aspect and the second aspect.

[0076] In the method for manufacturing a sample 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 method). That is, in the method for manufacturing a sample according to one aspect, a metal compound gas is supplied to the surface of the sample and chemically bonded, and then the metal compound gas is removed and an oxidizing agent gas is supplied to the surface of the porous material. Therefore, it is possible to prevent the metal compound gas and the oxidizing agent gas from reacting with each other in the air in the reaction chamber. In addition, since the metal compound gas and the oxidizing agent gas are supplied in a gaseous state up to the surface of the sample, 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 FIG. 2, in the method for manufacturing a sample (ALD method) according to one aspect of the present invention, it is expected that a uniform layer can be formed not only on the outer surface of the sample but also on the inner surface of the pores present in the sample. On the other hand, for example, as shown in FIG. 2, in the chemical vapor deposition method (CVD method), since the metal compound gas and the oxidizing agent gas are reacted in the reaction chamber, it is not easy to introduce metal oxide particles into the pores inside the sample. Similarly, in the physical vapor deposition method (PVD method), it is not easy to introduce charged metal particles to the inner surface of the pores present on the surface of the sample.

[0078] It is expected that the sample manufactured by the manufacturing method according to one aspect of the present invention can form a uniform layer up to the inner surface of the pores present in the sample. Therefore, by combining X-ray analysis with electron microscope observation and using a dynamic contour model, the structure in the sample section can be extracted as a contour in the electron microscope tomogram, and it is expected that sample observation by three-dimensional mapping can be realized.

[0079] Therefore, according to the method for manufacturing a sample and the method for observing a sample according to one aspect of the present invention, it is expected that the structure of the inner surface of the pores inside the sample can be three-dimensionally visualized not only on the outer surface of the sample without grinding the sample.

[0080] 〔Summary〕 A method for manufacturing a sample according to one aspect of the present invention includes a first treatment step of forming a layer of the metal compound by attaching a gaseous metal compound to the surface of a material, and a second treatment step of forming a metal oxide or a metal layer from the layer of the metal compound by reacting the metal compound with a gaseous oxidant, and the material includes a particulate material.

[0081] In the method for manufacturing a sample according to one aspect of the present invention, it is preferable that the particulate material is a particulate porous material.

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

[0083] In the method for manufacturing a sample according to one aspect of the present invention, it is more preferable that the carbon material is graphite.

[0084] In the method for manufacturing a sample according to one aspect of the present invention, the material may include the particulate material and further a resin, and a layer of the metal oxide or the metal may be formed on the surface of the material.

[0085] In the method for manufacturing a sample according to one aspect of the present invention, the resin may be an ionomer.

[0086] In the method for manufacturing a sample according to one aspect of the present invention, it is more preferable that the metal included in the metal compound is any one metal selected from the group consisting of hafnium, zirconium, aluminum, silicon, and titanium.

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

[0088] In the method for manufacturing a sample according to one aspect of the present invention, it is more preferable that the gaseous oxidant is one or more selected from the group consisting of water vapor, ozone, and oxygen plasma.

[0089] In the method for producing a sample according to one aspect of the present invention, in the first treatment step and the second treatment step, the metal compound and the oxidizing agent may be reacted at a temperature in the range of 20°C to 200°C.

[0090] In the method for producing a sample according to one aspect of the present invention, it is more preferable to repeat the first treatment step and the second treatment step a plurality of times as a series of steps.

[0091] In the method for producing a sample according to one aspect of the present invention, it is more preferable that the series of steps further includes a purging step of purging unreacted substances of the gaseous metal compound and unreacted substances of the gaseous oxidizing agent with an inert gas, respectively, between after the first treatment step and before the second treatment step and between after the second treatment step and before the first treatment step.

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

[0093] In the method for observing a sample according to one aspect of the present invention, it is more preferable that the electron microscope is a scanning transmission electron microscope.

[0094] In the method for observing a sample according to one aspect of the present invention, the sample may be observed with the electron microscope at an acceleration voltage in the range of 30 to 300 kV.

[0095] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in 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.

Example

[0096] An observation sample of Example 1 was prepared by forming a metal oxide layer on the catalyst layer collected from the MEA, and its surface state was observed with a scanning transmission electron microscope.

[0097] (Preparation of Observation Sample) The catalyst layer of MEA (Membrane Electrode Assembly; trade name Hydrogen Air MEA-5layer 10×10cm, manufactured by Mauvick Co., Ltd.) was scraped off by using a spatula to obtain about 5 mg, and mixed with about 5 mL of ethanol in a sample bottle to obtain a mixed solution. Next, ultrasonic dispersion was performed on the obtained mixed solution for about 1 minute to obtain an ethanol dispersion of the catalyst layer.

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

[0099] (ALD Treatment) The mesh on which the sample was placed was fixed in the reaction chamber of an ALD apparatus AT-400 (manufactured by Anric Technologies), and ALD treatment was performed. The conditions of the ALD treatment are as follows. Precursor gas: Trimethylaluminum (TMA) Oxidizing agent gas: H2O Purge gas: N2 Reaction chamber temperature: 150 °C A series of steps in which the precursor gas treatment step, the precursor gas purge step, the water vapor gas treatment step, and the water vapor gas purge step are continuously performed is defined as one cycle, and this cycle was performed 20 times to perform a total treatment 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 Water vapor treatment: 0.5 seconds, water vapor flow rate 0.75 SCCM Purge gas treatment: 10 seconds, purge gas flow rate 96 SCCM This series of treatments was performed in a reaction chamber at a temperature of 150 °C and a vacuum degree of 225 mPa, and repeated 20 cycles. The total reaction time was about 30 minutes. By the ALD treatment, an observation sample coated with a metal film of about 2 nm was obtained.

[0100] (HAADF-STEM observation) Using a scanning transmission electron microscope JEM-ARM200F (manufactured by JEOL Ltd.), STEM observation of the observation sample of Example 1 was performed. The acceleration voltage in the STEM observation was 200 kV, and the observation magnification was set to 1,000,000 times. The observation sample was photographed. The STEM photograph of the catalyst layer treated by ALD under this condition is shown in FIG. 3. FIG. 4 shows the STEM photograph of the catalyst layer before the treatment.

[0101] In FIG. 3, since the surface of the particulate porous material in the catalyst layer was covered with a metal oxide film, the surface structure of the particles was clearly visible. Also, since the ionomer was protected by the metal oxide film, the ionomer could be observed together with the porous material as shown by the broken line portion in FIG. 3.

[0102] In FIG. 4, the detailed surface structure of the particulate porous material in the catalyst layer was not observed, and also, as shown by the broken line portion in FIG. 4, the ionomer that should exist between the porous materials was not observed, and it is considered that this is because the ionomer was destroyed by the electron beam.

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

[0104] As a material, 300 m 2 Except for using carbon powder having a specific surface area of / g, in the same manner as in Example 1, an observation sample was prepared, ALD treatment was performed, and HAADF-STEM observation was performed. The STEM photograph of the ALD-treated carbon powder is shown in FIG. 5. The STEM photograph of the carbon powder before the treatment is shown in FIG. 6.

[0105] As shown in FIGS. 5 and 6, the observation sample subjected to ALD treatment has a large contrast imparted to the contour of the carbon material as compared with the observation sample not subjected to ALD treatment, and the surface state could be clearly observed. Since the surface state can be observed clearly in this way, the method for manufacturing a sample according to one aspect of the present invention is expected to be useful for a sample used in a method for observing the three-dimensional structure of a sample, such as 3D-STEM.

Claims

[Claim 1] a first treatment step of depositing a gaseous metal compound on a surface of a material to form a layer of said metal compound; a second process step of forming a metal oxide or metal layer from the layer of metal compound by reacting the metal compound with a gaseous oxidizing agent; A method for producing a sample, the material comprising a particulate material.

Images