Method for preparing transmission electron microscopy samples

Abstract

To enable more reliable and efficient preparation of a transmission electron microscopy sample from a sheet-like sample with pores.SOLUTION: A method for preparing a transmission electron microscopy sample is provided, the method comprising a preparation step of preparing a sheet-like sample having pores therein, coating step of coating a surface of the sheet-like sample with an uncured liquid resin, and a curing step of curing the liquid resin while applying a load in a thickness direction to the sheet-like sample having the liquid resin coating to form a temporary molded body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for preparing a specimen for a transmission electron microscope. [Background technology]

[0002] Samples for observation with a transmission electron microscope (TEM) must be thinned to a thickness that allows electron beams to pass through, for example, 100 nm or less. Thinning can be performed using, for example, a focused ion beam (FIB) or an Ar ion milling device.

[0003] Before processing the sample into thin sections, it is necessary to perform a specific pretreatment depending on the form it is in. For example, if the sample is in powder form, it has been proposed to mix the sample with a liquid resin, fill the holes in a single-hole mesh, and then harden the mixture (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-294594 Summary of the Invention [Problem to be solved by the invention]

[0005] Thin, void-filled sheet samples are also being considered for TEM observation. To process such sheet samples into TEM specimens, the following pretreatment process can be considered. For example, a liquid resin is first applied to the sheet sample and attached to a base substrate. The surface of the sheet sample is then polished to a smooth surface. A cover glass is then attached to the polished surface to create a laminate. TEM specimens can be prepared by cutting a specimen piece approximately 100 μm thick from the laminate using, for example, a diamond cutter, and then thinning the specimen piece.

[0006] However, when the sheet sample is subjected to the above-mentioned pretreatment, the sheet sample may be warped and fixed. This is because the sheet sample, which has voids, easily absorbs the liquid resin, causing it to swell and create stress inside.

[0007] If a sheet sample is fixed in a warped state, excessive grinding of the warped edge of the sheet sample may occur when the sheet sample is exposed to the surface and polished to a smooth surface. This tends to narrow the area that can be observed with a TEM. If the observation area becomes too narrow, accurate TEM observations cannot be performed. Furthermore, the amount of grinding required to expose the sheet sample increases, lengthening the time required for pretreatment.

[0008] The present invention has been made in view of the above-mentioned problems, and aims to provide a technique for more reliably and efficiently preparing a transmission electron microscope specimen from a sheet-like specimen having voids. [Means for solving the problem]

[0009] A first aspect of the present invention is a preparation step of preparing a sheet-like sample having voids therein; a coating step of coating an uncured liquid resin on the surface of the sheet-like sample; and a curing step of curing the liquid resin while applying a load in the thickness direction to the sheet sample to which the liquid resin has been applied, to form a provisional molded body. A method for preparing a sample for a transmission electron microscope.

[0010] A second aspect of the present invention is a method for producing a composition comprising the steps of: The liquid resin is at least one of a thermosetting resin and a room temperature curing resin.

[0011] A third aspect of the present invention is a method for producing a composition comprising the steps of: The thermosetting resin is an epoxy resin.

[0012] A fourth aspect of the present invention is the second aspect, The room temperature curable resin is a photocurable acrylic resin or a cyanoacrylate resin.

[0013] A fifth aspect of the present invention is the method according to any one of the first to fourth aspects, The thickness of the sheet sample is 20 μm or more and 100 μm or less.

[0014] A sixth aspect of the present invention is the method according to any one of the first to fifth aspects, The size of the voids in the sheet sample is 1 μm or more and 10 μm or less.

[0015] A seventh aspect of the present invention is any one of the first to sixth aspects, a filling step of placing a spacer on a base substrate, placing the temporary molded body on the bottom of a recess formed by the base substrate and the spacer, and then filling the recess with uncured liquid resin and curing it to form a filling body; a polishing step of polishing the surface of the filler opposite to the base substrate so that the sheet-like sample is exposed, thereby forming a polished body; and a thinning step of laminating a glass member onto the polishing surface of the polishing body and then thinning the glass member. [Effects of the Invention]

[0016] According to the present invention, a transmission electron microscope sample can be more reliably and efficiently prepared from a sheet-like sample having voids. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a flow of a method for preparing a transmission electron microscope sample according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view for explaining a case where a liquid resin is applied to a sheet-like sample and then heated. [Figure 3] FIG. 3 is a schematic cross-sectional view showing the structure of the temporary compact. [Figure 4] Figures 4(a) to (c) are diagrams for explaining the processing of a temporary molded body into a TEM sample, where (a) is a schematic cross-sectional view showing the case where the temporary molded body is filled with resin, (b) is a view showing the case where the filled body is polished, and (c) is a view showing the case where a glass member is bonded to the polished filled body. [Figure 5] FIG. 5 is a schematic cross-sectional view showing a sheet sample coated with a liquid resin and attached to a support substrate. [Figure 6] FIG. 6 is a schematic cross-sectional view showing the sheet sample of FIG. 5 when it is polished up to the broken line. DETAILED DESCRIPTION OF THE INVENTION

[0018] As described above, when processing a sheet sample with voids into a TEM sample, the sheet sample coated with uncured liquid resin is placed on a base substrate and then bonded by curing the liquid resin. At this time, as shown in Figure 5, the sheet sample 10' absorbs the liquid resin, swells, and becomes warped. If the liquid resin is cured in this state to form cured resin 21', the sheet sample 10' will be fixed in its warped shape.

[0019] The surface of the fixed sheet sample 10' is covered with the cured resin 21' and its thickness is not uniform. Therefore, the surface must be polished to expose the sheet sample 10' and make the thickness uniform. For example, polishing is performed up to the dashed line shown in Figure 5. As a result, the sheet sample 10' is polished, for example, as shown in Figure 6. During this process, the curved edges of the sheet sample 10' are scraped off, so the area of ​​the sheet sample 10' exposed on the polished surface becomes smaller than the original area of ​​the sheet sample 10'. If the exposed area of ​​the sheet sample 10' becomes too small, the TEM observation field cannot be secured, and accurate observation cannot be performed. In this case, it becomes necessary to prepare a new sheet sample 10' and repeat the pretreatment process. Furthermore, the amount of polishing required to obtain the desired polished surface increases, resulting in a longer polishing time.

[0020] To solve this problem, the inventors conducted research and found that it is effective to apply uncured liquid resin to a sheet-like sample and then cure the liquid resin while applying a load to the sheet-like sample to suppress warping. This allows the sheet-like sample to be processed into a provisionally molded body with minimal warping. Furthermore, the provisionally molded body allows for more reliable and efficient preparation of TEM samples.

[0021] The present invention was made based on the above findings.

[0022] <One embodiment of the present invention> A method for preparing a transmission electron microscope specimen according to one embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 is a diagram showing the flow of a method for preparing a transmission electron microscope specimen according to one embodiment of the present invention.

[0023] (Preparation process S1) First, a sheet-like sample 10 is prepared as the sample to be observed. The sheet-like sample 10 is porous and has voids therein. The voids are, for example, spherical, and the void size is preferably 5 μm or more and 10 μm or less in maximum diameter. The thickness of the sheet-like sample 10 is not particularly limited, but is preferably, for example, 20 μm or more and 100 μm or less. The sheet-like sample 10 is formed from, for example, an inorganic material or an organic material. An example of such a sheet-like sample 10 is a porous sintered body obtained by sintering powder.

[0024] (Coating process S2) Next, an uncured liquid resin 20 to be applied to the sheet-like sample 10 is prepared. The liquid resin 20 is a resin that is liquid at room temperature and that is cured, for example, by heat, light, or moisture. Examples of such liquid resins 20 include thermosetting resins and room-temperature curing resins. Here, room-temperature curing resins refer to resins that are cured at room temperature without the use of heat. Room-temperature curing resins refer to resins that do not require heating for curing and that are cured in a room-temperature environment. The curing temperature is not particularly limited, but is preferably, for example, between 10°C and 40°C. Examples of room-temperature curing resins include photocuring resins that are cured by irradiation with light, and moisture-curing resins that are cured by reacting with moisture in the air.

[0025] As the thermosetting resin, for example, a heat-curable epoxy resin can be used. The curing temperature of the thermosetting resin is preferably, for example, 80°C or higher and 120°C or lower, from the viewpoint of suppressing deterioration of the sheet-shaped sample 10 during heat curing. Compared to photocurable resins and the like, thermosetting resins are less likely to shrink during curing, and therefore deformation of the sheet-shaped sample 10 can be suppressed.

[0026] As the room temperature curing resin, a photocurable resin or a moisture curable resin can be used. As the photocurable resin, for example, a photocurable acrylic resin such as epoxy acrylate or urethane acrylate can be used. As the moisture curable resin, for example, a cyanoacrylate resin can be used. Cyanoacrylate resin has a carbonyl group and can be cured by reacting and polymerizing when it comes into contact with moisture. Since the room temperature curable resin can be cured without heating, a material that is sensitive to heat can be selected for the sheet-like sample 10.

[0027] Next, a liquid thermosetting resin is applied to the surface of the sheet sample 10 as the uncured liquid resin 20. The liquid resin 20 is preferably applied so as to cover at least the surface of the sheet sample 10. The liquid resin 20 may be absorbed into the sheet sample 10 and fill any voids. The amount of the applied liquid resin 20 is sufficient to fix the shape of the sheet sample 10 when the liquid resin 20 is cured, and is preferably sufficient to fill any voids in the sheet sample 10. Any conventionally known application method can be used.

[0028] (Curing process S3) Next, the liquid resin 20 is hardened while a load is applied in the thickness direction to the sheet sample 10 on which the liquid resin 20 has been applied.

[0029] 2, the sheet sample 10 coated with the liquid resin 20 is placed on a support member 31, and then sandwiched between a pair of sandwiching members 32, 32. Then, a pressure member 33 is used to apply a load to the sheet sample 10 from one of the sandwiching members 32.

[0030] The sheet sample 10 may be warped due to swelling caused by absorbing the liquid resin 20. In addition, the sheet sample 10 may be taken from a curled sample and may have a warped shape to begin with, and the warping may become more pronounced due to the absorption of the liquid resin 20. In this regard, the shape of the sheet sample 10 can be corrected to be flat by applying a load in the thickness direction of the sheet sample 10.

[0031] In this embodiment, the liquid resin 20 is cured while a load is applied to the sheet sample 10. This curing method may be changed as appropriate depending on the type of liquid resin 20. In this embodiment, the liquid resin 20 is a thermosetting resin, so heating is performed. As a result, as shown in FIG. 3, the liquid resin 20 applied to the sheet sample 10 is cured to form a temporary molded body 11. The temporary molded body 11 comprises a flat sheet sample 10 and a cured resin 21 present on the surface and inside of the sheet sample 10, which are integrally formed. The sheet sample 10 is fixed in a flat shape by the cured resin 21. After curing, the clamping member 32 and the like are removed, and the temporary molded body 11 is peeled off from the support member 31.

[0032] The support member 31 is not particularly limited as long as it can support the sheet sample 10 and has appropriate elasticity, and for example, a silicon substrate can be used. The clamping member 32 is not particularly limited as long as it can clamp the sheet sample 10, and for example, a glass substrate can be used. The pressing member 33 is not particularly limited as long as it can apply a load to the sheet sample 10, and for example, a stainless steel plate can be used as a weight. Note that the pressing method is not limited to the method using the pressing member 33 shown in FIG. 2, and any known method can be used. In addition, the clamping member 32 may be in contact with the sheet sample 10 and the support member 31 via a release member (not shown), such as a silicone film, to prevent adhesion between the clamping member 32 and the sheet sample 10.

[0033] The heating method may be any known method as long as it is capable of heating the liquid resin 20 to a temperature at which the liquid resin 20 can be cured. For example, a heating furnace may be used. The heating temperature may be adjusted appropriately depending on the curing temperature of the liquid resin 20.

[0034] The provisionally formed body 11 may be sliced ​​as is, but from the viewpoint of providing for TEM observation, it is preferable to carry out the filling step S4, polishing step S5, and thinning step S6 described below. A specific explanation will be given below using Figures 4(a) to 4(c). Figures 4(a) to 4(c) are diagrams for explaining the processing of the provisionally formed body 11 into a TEM sample. Specifically, Figure 4(a) is a schematic cross-sectional view showing the case where the provisionally formed body is filled with resin, Figure 4(b) is a schematic cross-sectional view showing the case where the filled body is polished, and Figure 4(c) is a schematic cross-sectional view showing the case where a glass member is bonded to the polished filled body.

[0035] (Filling process S4) 4(a), spacers 42 are placed on the main surface of the base substrate 41. For example, two spacers 42 may be placed on the main surface of the base substrate 41 so as to face two sides of the main surface. A recess 43 is formed by the base substrate 41 and the spacers 42. This recess 43 becomes a region for accommodating the temporary molded body 11.

[0036] Next, the temporary molded body 11 is placed on the bottom of the recess 43 on the main surface of the base substrate 41. For example, the temporary molded body 11 may be adhered and fixed to the base substrate 41 using an adhesive. Thereafter, the recess 43 is filled with uncured liquid resin 20. A thermosetting epoxy resin or the like can be used as the liquid resin 20. The filled liquid resin 20 is then heated and cured to form a cured resin 21. In this way, the filling body 12 is obtained.

[0037] Since the shape of the temporary molded body 11 is fixed by the cured resin 21, warping of the temporary molded body 11 can be suppressed when filling with liquid resin. Therefore, the shape of the temporary molded body 11 can be maintained flat in the filling body 12.

[0038] The base substrate 41 is a member that supports the provisionally formed body 11. The base substrate 41 is preferably made of a component that does not cause contamination, unlike the components contained in the sheet-like sample 10. For example, a silicon substrate can be used as the base substrate 41. The thickness of the base substrate 41 is not particularly limited, and is preferably, for example, 350 μm to 500 μm.

[0039] The spacer 42 is a member having a thickness that allows the formation of a recess 43 deep enough to accommodate the sheet sample 10. As the spacer 42, for example, a glass member such as a cover glass can be used.

[0040] (Polishing process S5) Next, as shown in FIG. 4(b), the surface of the filler 12 opposite the base substrate 41 is polished so that the provisionally formed body 11 is exposed. As shown in FIG. 4(a), when a sample with one raised surface and uneven thickness is directly sliced, the grinding balance between the raised and non-raised sides may be lost. This may result in errors in the TEM observation results. Therefore, in the polishing step S5, the raised side is polished and flattened so that the provisionally formed body 11 is exposed. This results in a polished body 13.

[0041] In this embodiment, the sheet sample 10 is processed in advance into a temporary compact 11 and its shape can be fixed flat, so that polishing can be performed while ensuring a large area of ​​the sheet sample 10 compared to polishing a warped sheet sample 10' as shown in Fig. 5. Moreover, the amount of polishing required to expose the sheet sample 10 (polishing thickness) can be reduced.

[0042] In the polishing step S5, the filler 12 is preferably polished so as to remove a portion of the provisionally formed body 11 in the thickness direction. This makes it possible to more reliably expose the sheet sample 10 on the surface of the polished body 13. Note that, as a polishing method, a conventionally known method such as mechanical polishing can be used. For mechanical polishing, for example, a precision surface grinder (HLA-2, manufactured by JEOL Ltd.) can be used.

[0043] 4(c), a glass member 51 is attached to the polishing surface 13a of the polishing body 13 so as to cover the entire surface, thereby forming a laminate 14. A so-called cover glass can be used as the glass member 51, and its thickness may be, for example, 100 μm or more and 150 μm or less.

[0044] (Thinning process S6) Next, a sample piece is cut from the laminate 14 to a thickness of about 100 μm using, for example, a diamond cutter, etc. This sample piece is introduced into a thin section processing device and thinned to prepare a TEM sample. At this time, it is preferable to perform thin section processing so that the thickness of the thin section is, for example, 10 nm to 100 nm.

[0045] As a thinning device, for example, a focused ion beam device (FIB) or an Ar ion milling device can be used. Among them, a cryo-ion slicer (CIS), which is a type of Ar ion milling device, is preferred. Compared to an FIB, a CIS can thin a wider area. This allows a wider observation field to be secured, and a field suitable for observation can be more reliably obtained.

[0046] In this way, a sample for TEM observation is obtained.

[0047] <Effects of this embodiment> According to this embodiment, one or more of the following effects are achieved.

[0048] (a) In this embodiment, a thermosetting resin is applied as the liquid resin 20 to a sheet-like sample 10 having internal voids, and then the sample is heated while a load is applied in the thickness direction to form a temporary compact 11. The sheet-like sample 10 may absorb the liquid resin 20 and warp, but applying a load to the sheet-like sample 10 to harden the liquid resin 20 in a flat state with minimal warping can fix the shape of the temporary compact 11 flat. With this temporary compact 11, when polishing the sheet-like sample 10 after bonding it to the base substrate 41, excessive scraping of the sheet-like sample 10 is avoided, ensuring a wide exposed area of ​​the sheet-like sample 10. As a result, TEM samples suitable for TEM observation can be more reliably and efficiently prepared.

[0049] (b) The thinner the sheet sample 10, the more likely it is to warp. However, since the sheet sample 10 coated with the liquid resin 20 is heated under load to fix its shape flat, a TEM sample can be prepared more reliably and efficiently even for a sheet sample 10 having a thickness of 10 μm or more and 100 μm or less.

[0050] (c) As the size of the voids in the sheet sample 10 increases, the sample absorbs the liquid resin 20 more easily, and swelling can cause more pronounced warping. In this regard, the sheet sample 10 coated with the liquid resin 20 is heated under load to fix its shape flat, so that even if the size of the voids is between 1 μm and 10 μm, a TEM sample can be prepared more reliably and efficiently.

[0051] (d) It is preferable to use a thermosetting epoxy resin that is liquid at room temperature as the liquid resin 20. Epoxy resin shrinks very little when cured and is not easily deteriorated by electron beam irradiation, allowing for more accurate observation of the TEM sample.

[0052] (e) It is preferable that the temporary compact 11 is processed into the filler 12 in the above-mentioned filling step S4, and then the filler 12 is processed into the polished body 13 in the polishing step S5. The polished body 13 is easier to handle than when the temporary compact 11 is directly sliced, and the thinning process can be performed more accurately. This makes it possible to more reliably obtain the above-mentioned effect (a).

[0053] (f) In the above-described embodiment, the temporary compact 11 is formed on a silicon substrate serving as the support member 31 in the hardening step S3, and after peeling, the temporary compact 11 is placed on a silicon substrate serving as the base substrate 41 in the filling step S4. In other words, the member on which the temporary compact 11 is placed is changed from the support member 31 to the base substrate 41. As a result, the hardening step S3 employs a support member 31 that can be heated while applying a load, while the filling step S4 employs a base substrate 41 that has a size that allows it to be easily introduced into the thin section processing device in the thinning step S6. As a result, the processing required for introduction into the thin section processing device can be omitted, thereby improving the efficiency of TEM sample preparation.

[0054] <Other Embodiments of the Present Invention> Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention.

[0055] In the above embodiment, a case where a thermosetting resin is used as the liquid resin 20 when forming the temporary molded body 11 and the filler 12 has been described, but a room temperature curable resin may also be used. Below, the cases where a photocurable resin and a moisture curable resin are used as the room temperature curable resin will be described.

[0056] When a photocurable resin is used as the liquid resin 20, the sheet-like sample 10 is coated with the photocurable resin, then placed on a support member 31, and sandwiched between a pair of sandwiching members 32, 32. Here, the support member 31 and sandwiching member 32 are made of transparent materials such as glass plates. Light (ultraviolet rays) is then irradiated onto the sheet-like sample 10 through the support member 31 and sandwiching member 32. This hardens the photocurable resin, forming the provisional compact 11. To produce the filler 12 from the provisional compact 11, the provisional compact 11 is placed on the bottom of the recess 43 and filled with the photocurable resin, as in the above-described embodiment. The filled photocurable resin is then irradiated with ultraviolet rays to harden it, forming the filler 12. When a photocurable resin is used, a transparent material with mass, such as a piece of glass, may be used for the pressing member 33. If the pressing member 33 is a transparent material, the degree of freedom in light irradiation is improved.

[0057] When a moisture-curable resin is used as the liquid resin 20, the moisture-curable resin is applied to the sheet sample 10, and then the sheet sample 10 is left to stand while a load is applied thereto, as shown in FIG. 2. At this time, the moisture-curable resin reacts with moisture in the air to harden, thereby forming the filler 12. To produce the filler 12 from the temporary compact 11, the temporary compact 11 is placed on the bottom of the recess 43 and filled with the moisture-curable resin, as in the above-described embodiment. By leaving it for a predetermined time, the filled moisture-curable resin hardens, and the filler 12 can be formed.

[0058] Room-temperature curable resins do not require heating for hardening, so a heat-sensitive material can be selected for the sheet sample 10. Furthermore, the hardening time can be shortened compared to thermosetting resins. This improves the efficiency of preparing samples for transmission electron microscopes. Room-temperature curable resins tend to shrink significantly when hardened, but in this embodiment, the sheet sample 10 is thin, so the effects of shrinkage due to hardening can be suppressed.

[0059] In the above embodiment, the same thermosetting resin is used as the liquid resin 20 when forming the temporary molded body 11 and when forming the filler 12, but the present invention is not limited to this. Different types of liquid resin 20 may be used when forming the temporary molded body 11 and the filler 12. For example, different types of liquid resin 20 may be used, such as using a thermosetting resin when forming the temporary molded body 11 and using a photocurable resin when forming the filler 12. [Explanation of symbols]

[0060] 10 Sheet sample 11 Temporary molded body 12 Filler 13 Polishing body 13a Polished surface 14 Laminate 20 Liquid Resin 21 Cured resin 31 Support member 32 Clamping member 33 Pressing member 41 Base substrate 42 spacer 43 Recess 51 Glass components

Claims

1. a preparation step of preparing a sheet-like sample having voids therein; a coating step of coating an uncured liquid resin on the surface of the sheet-like sample; and a curing step of curing the liquid resin while applying a load in the thickness direction to the sheet sample to which the liquid resin has been applied, to form a provisional molded body. Methods for preparing specimens for transmission electron microscopy.

2. The liquid resin is at least one of a thermosetting resin and a room temperature curing resin.

2. A method for preparing a transmission electron microscope sample according to claim 1.

3. The thermosetting resin is an epoxy resin.

3. The method for preparing a transmission electron microscope sample according to claim 2.

4. The room temperature curable resin is a photocurable acrylic resin or a cyanoacrylate resin.

3. The method for preparing a transmission electron microscope sample according to claim 2.

5. The thickness of the sheet sample is 20 μm or more and 100 μm or less.

2. A method for preparing a transmission electron microscope sample according to claim 1.

6. the size of the voids in the sheet sample is 1 μm or more and 10 μm or less; 2. A method for preparing a transmission electron microscope sample according to claim 1.

7. a filling step of placing a spacer on a base substrate, placing the temporary molded body on the bottom of a recess formed by the base substrate and the spacer, and then filling the recess with uncured liquid resin and curing it to form a filling body; a polishing step of polishing the surface of the filler opposite to the base substrate so that the sheet-like sample is exposed, thereby forming a polished body; A thinning step of laminating a glass member to the polishing surface of the polishing body and then thinning the glass member.

3. A method for preparing a transmission electron microscope sample according to claim 1.

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