Sample pretreatment method

Abstract

To prevent trouble from occurring easily in observation and machining by applying radiations regardless of an object sample prepared by a material containing an element having a high ionization tendency.SOLUTION: A pretreatment method of a sample includes: a setting procedure for setting an object sample to a support; an insulation procedure for coating the surface of the support and the object sample set to the support with a material having an electrical insulation performance; a conductive procedure for coating the surfaces of the support and the object sample coated with the outer insulation layer with a conductive layer. In the setting procedure, the object sample is set to the support via a suppression layer composed of a material having low ion conductivity in its front and back direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pretreatment method for pretreating a sample when observing or processing the sample by irradiating the sample with radiation. [Background Art]

[0002] Conventionally, observation and processing of a target sample have been performed by irradiating the target sample with radiation such as electron beams or X-rays, and various countermeasures have been proposed to avoid problems caused by charge-up of the target sample accompanying the process, such as blurred observation images and insufficient processing. For example, a conductive substance is formed on the surface of a sample to be observed with an electron microscope (see Patent Document 1). [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 10-104142 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, when a target sample is prepared from a material containing an element with a high ionization tendency (such as lithium or sodium) like solid electrolytes used in secondary batteries, even if problems caused by charge-up can be avoided, there is a problem that other problems such as compositional deviation and structural change of the target sample occur due to the migration of ions from the target sample to the side of a support that supports the target sample. In an environment where radiation is irradiated, the generation of ions is promoted by cascade damage to the target sample, so the above-mentioned problems are likely to occur.

[0005] The present invention has been made to solve such problems, and an object of the present invention is to make it less likely that problems occur during observation or processing by irradiating radiation even when the target sample is prepared from a material containing an element with a high ionization tendency. [Means for solving the problem]

[0006] The first step in solving the above problem is a sample pretreatment method comprising: a setting procedure for setting the target sample on a support; an insulating procedure for coating the surface of the support and the target sample set on the support with an insulating layer made of a material having electrical insulating properties; and a conductive procedure for coating the surface of the support and the target sample coated with the insulating layer with a conductive layer, wherein in the setting procedure, the target sample is set on the support via an inhibitory layer made of a material with low ionic conductivity in the front-to-back direction.

[0007] This phase may be as shown in the second phase below. In the second phase, the procedure includes a suppression step of coating the surface of the support with the suppression layer, and in the setting step, the target sample is set on the support coated with the insulating layer.

[0008] Furthermore, each of the above aspects may be as shown in the third aspect below. In the third aspect, when the target sample is a solid electrolyte, in the suppression procedure, a layer made of amorphous oxide material is used as the suppression layer, and the surface of the support is coated with the suppression layer; in the insulation procedure, a layer made of amorphous oxide material is used as the insulation layer, and the surfaces of the support and the target sample are coated with the insulation layer; and in the conductivity procedure, a layer made of carbon material is used as the conductivity layer, and the surfaces of the support and the target sample are coated with the conductivity layer.

[0009] In the sample pretreatment methods described above, the target sample is set with a suppression layer that has low ion conductivity in the front-to-back direction interposed between it and the support. As a result, when observing or processing the target sample by irradiation with radiation, the movement of ions from the target sample to the support is suppressed, making it less likely for defects such as compositional deviations or structural changes in the target sample to occur.

[0010] Furthermore, in this phase, an insulating layer with electrical insulating properties is interposed between the target sample and the conductive layer. This suppresses conductivity and ion movement from the target sample to the conductive layer, resulting in less likelihood of problems occurring due to ion movement in addition to charge buildup. [Brief explanation of the drawing]

[0011] [Figure 1] A flowchart illustrating the sample pretreatment procedure described in this disclosure. [Figure 2] This disclosure shows a support and a cross-sectional view of the main part of the target sample, illustrating how the sample is pre-treated. [Figure 3] STEM image (a) of the sample observed in the example of this disclosure, and EDS image (b) (1 / 2) of the sample analyzed by EDS. [Figure 4] STEM image (a) and EDS image (b) of the sample observed in the example of this disclosure (2 / 2) [Modes for carrying out the invention]

[0012] Below, as an embodiment of the present disclosure, a pretreatment method for pre-treating a sample before observation or processing of the sample by irradiation with radiation will be described with reference to the drawings. In this embodiment, the pretreatment method for pre-treating a target sample before observation of the target sample by irradiation with an electron beam using a transmission electron microscope (TEM) will be illustrated. Here, the target sample is an oxide-based solid electrolyte composed of a material containing an element with a high ionization tendency, such as sodium or lithium.

[0013] (1) Sample pretreatment method; Figure 1 In this pretreatment method, first, an "inhibition procedure" is performed in which the surface of the support for supporting the target sample is coated with an inhibitory layer (s110). Here, as shown in Figures 2(a) and 2(b), a layer made of a material with low ionic conductivity in the front-to-back direction is designated as the inhibitory layer 10, and the surface of the support 1 is coated with this inhibitory layer 10.

[0014] In this embodiment, alumina, an amorphous oxide material with few atomic defects and valency changes, is selectively used as the material for the suppression layer 10, i.e., a material with low ionic conductivity in the front-to-back direction. Other materials such as silicon nitride can also be used.

[0015] Next, a "setting procedure" is performed in which the target sample is set on the support coated with the suppression layer (s120). Here, as shown in Figure 2(c), the target sample 2 is set on the support 1 via the suppression layer 10 coated thereon by placing the target sample 2 on the support 1 (the carbon film constituting the support 1 in this embodiment).

[0016] For coating the suppression layer 10, well-known methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and atomic layer deposition (ALD) are used.

[0017] Next, an "insulation procedure" is performed in which the surface of the support and the target sample set thereon are coated with an insulating layer (s130). Here, as shown in Figure 2(d), a layer made of a material having electrical insulating properties is used as the insulating layer 20, and the surface of the support 1 and the target sample 2 are coated with this insulating layer 20.

[0018] In this embodiment, alumina, the same material used for the suppression layer 10, is selected as the material for the insulating layer 20. Other materials, such as lithium oxide, could also be used.

[0019] Then, a "conductive layer forming step" is performed, in which the surfaces of the insulating layer-coated support and the target sample are coated with a conductive layer (s140). Here, as shown in Fig. 2(e), a layer formed of a conductive material is used as the conductive layer 30, and the conductive layer 30 coats the surfaces of the support 1 and the target sample 2 together with the insulating layer 20.

[0020] In the present embodiment, the conductive layer 30 formed of a conductive material is coated on the surfaces of the support 1 and the target sample 2 by the same method as described above. As a material for the conductive layer 30, carbon, which is a conductive material, is used for the selected body. A conductive material other than carbon can also be used as this material.

[0021] In this way, a pretreated target sample 2 set on the support 1 is prepared as an observation object for a transmission microscope.

[0022] Note that, in the pretreatment method for observation with a transmission electron microscope as in the present embodiment, if each of the above-described layers is too thick, it becomes difficult for electron beams to transmit through during observation, whereas if each layer is too thin, the respective functions as a layer cannot be exhibited. Therefore, in the present embodiment, the film thickness is adjusted such that the total thickness of all layers is 10 nm or less.

[0023] (2) Modified Example The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments in any way, and it goes without saying that various forms can be adopted as long as they fall within the technical scope of the present invention.

[0024] For example, in the above-described embodiment, the pretreatment method for pretreating a target sample when observing the target sample by irradiating it with an electron beam from a transmission electron microscope has been exemplified. However, it goes without saying that this pretreatment method can be used as a method for pretreating a target sample when processing the target sample by irradiating it with radiation such as X-rays.

[0025] Furthermore, in the above embodiment, an example was shown in which the surface of the support is coated with the suppression layer during the suppression procedure. However, the suppression procedure may also be configured to coat the surface of the target sample with the suppression layer instead of the support.

[0026] (3) Effects In the sample pretreatment method according to the above embodiment, the target sample 2 is set on the support 1 with a suppression layer 10 having low ion conductivity in the front-to-back direction interposed between it and the support 1 (see Figure 2). As a result, when observing or processing the target sample by irradiation with radiation, the movement of ions from the target sample 2 to the support 1 is suppressed, making it less likely for defects such as compositional deviations or structural changes in the target sample 2 to occur.

[0027] Furthermore, in this embodiment, an insulating layer 20 having electrical insulating properties is interposed between the target sample 2 and the conductive layer 30. As a result, conductivity and ion movement from the target sample 2 to the conductive layer 30 are suppressed, making it less likely for problems to occur due to ion movement in addition to charge buildup.

[0028] In this regard, the applicant has used an oxide-based fixed electrolyte containing sodium as the target sample and performed energy dispersive x-ray spectroscopy (EDS) analysis using a scanning transmission electron microscope (STEM) on observation target A, which was directly set on a support, and observation target B, which was set on a support after undergoing the above pretreatment method, and has confirmed that ion migration is suppressed by the above pretreatment method.

[0029] First, in observation target A, as shown in Figure 3, the support 1 (specifically, a lattice-like carbon grid) seen in the STEM image (bright-field image) (Figure 3(a)) also appears in the EDS image (Figure 3(b)) which maps the sodium component. This is a result of sodium ions moving from the target sample 2 to the support 1, and the sodium component that thus moved appears along the support 1. In other words, in observation target A, where the target sample is set directly on the support, ion movement cannot be suppressed.

[0030] On the other hand, in observation target B, as shown in Figure 4, support 1 (same as above) seen in the STEM image (bright-field image) (Figure 4(a)) does not appear in the EDS image (same as Figure 4(b)) which maps the sodium component. This is a result of suppression of the movement of sodium ions from target sample 2 to support 1. [Explanation of Symbols]

[0031] 1...Support, 2...Target sample, 10...Inhibition layer, 20...Insulating layer, 30...Conductive layer.

Claims

1. The setup procedure for placing the target sample on the support, An insulating procedure comprising coating the surface of the support and the target sample set on the support with an insulating layer made of a material having electrical insulating properties, The procedure comprises a conductive step of coating the surface of the support coated with the insulating layer and the surface of the target sample with a conductive layer, In the setting procedure described above, the target sample is set on the support via an inhibitory layer made of a material with low ionic conductivity in the front-to-back direction. Sample pretreatment method.

2. The procedure includes coating the surface of the support with the suppression layer, In the setting procedure, the target sample is set on the support coated with the suppression layer. The sample pretreatment method according to claim 1.

3. When the target sample is a solid electrolyte, In the suppression procedure described above, a layer composed of an amorphous oxide material is used as the suppression layer, and the surface of the support is coated with the suppression layer. In the insulation procedure described above, a layer composed of an amorphous oxide material is used as the insulating layer, and the surface of the support and the target sample are coated with this insulating layer. In the aforementioned conductive procedure, a layer made of carbon material is used as the conductive layer, and the surface of the support and the target sample are coated with this conductive layer. The sample pretreatment method according to claim 2.

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