JP6502646B2 - Preparation method of electrode / electrolyte interface sample and in-situ observation method of potential distribution - Google Patents

Description

  The present invention relates to an observation technique of an electric element, and more particularly to an in-situ observation technique of observing an electric element in an operating state.

  The electric double layer capacitor can be charged and discharged with a large current, and can have a larger capacity than other capacitors such as an electrolytic capacitor. Therefore, the electric double layer capacitor is expected as a high-performance power storage device used for regeneration of electric power in an electric vehicle, output stabilization when using natural energy power generation, and the like. However, the energy density of the electric double layer capacitor is not sufficiently high, and it is required to develop an electric double layer capacitor having a higher energy density. Development of such an electric double layer capacitor with high energy density can be promoted by optimization of the electrode structure etc. constituting the electric double layer capacitor, but in order to optimize the electrode structure etc., an electric double layer is formed It is important to understand the potential distribution near the electrode / electrolyte interface in the selected state.

JP, 2013-234855, A JP 2000-133186 A Yamamoto, Tanji, Hibino, Hirayama, "High-precision phase-shifting electron holography", electron microscope, The Japanese Society of Microscopy, 2001, Vol. 36, No. 1, p. 71-74

  The potential distribution in the substance can be observed using an electron holography technique (see, for example, Patent Document 1). However, in an electron holography microscope, a sample is usually disposed inside a high vacuum electron holography microscope. Therefore, when a general electric double layer capacitor is to be observed, the solvent used for the electrolyte is a column. As it evaporates internally, the sample loses its function as an electric double layer capacitor and may contaminate the inside of the electron holography microscope. Also, in recent years, it has been proposed to arrange a sample in a sample chamber separated from a vacuum by a thin film for keeping airtight, and to observe the sample in a state of being kept under a specific gas atmosphere (for example, Patent Document 2). According to this method, it is possible to suppress the evaporation of the solvent, but the size of the sample chamber is limited, and a technology for producing a sample that functions as an electric double layer capacitor that can be disposed in the sample chamber is established. I did not. This problem is not limited to a sample for in-situ observation of an electric double layer capacitor, but is common to a sample for in-situ observation of an electric element having an electrolytic solution such as a lithium battery.

  The present invention has been made to solve the conventional problems described above, and it is an object of the present invention to provide a technique for producing a sample capable of in-situ observation for observing an electric element having an electrolytic solution in an operating state. Do.

In order to achieve at least a part of the above object, the present invention can be realized as the following forms or application examples.
A method for producing a sample as one embodiment of the present invention is a method for producing a sample for in-situ observation by electron beam irradiation in which an electric element having an electrolytic solution is observed in an operating state,
Preparing an electrode body having a thin section capable of transmitting the electron beam and having a hole in the direction of travel of the electron beam formed in the thin section; and having an electrode section and a separator; A counter electrode body configured to be capable of bringing the separator into contact with the electrode body at a contact position separated in a direction different from the traveling direction of the electron beam is prepared, and the electrolyte is held in the hole. And the electrolytic solution is attached to the electrode body so that the electrolytic solution is continued from the hole to the contact position, and the separator is brought into contact with the contact position, so that the electrode portion is interposed through the separator. In contact with the electrolyte solution.
According to this configuration, the counter electrode body is brought into contact at a contact position separated from the hole of the electrode body in which the electrolytic solution is held in the direction different from the traveling direction of the electron beam. Observation is easier. In addition, since the electrode portion of the counter electrode body is in contact with the electrolytic solution continuous from the hole to the contact position via the separator, the sample can be operated as an electric element. Therefore, by observing the peripheral portion of the hole, it is possible to observe in situ the phenomenon that occurs in the vicinity of the interface between the electrode of the electric element in the operating state and the electrolytic solution.
Furthermore, by forming the holes in a thin section of a thickness that allows transmission of an electron beam, it becomes easier to perform in-situ observation using a transmission electron microscope or a transmission scanning electron microscope. In addition, since the counter electrode body contacts the position separated from the thin plate portion in which the hole is formed in a direction different from the traveling direction of the electron beam, the risk of damaging the thin plate portion when contacting the counter electrode body is reduced. can do.

Application Example 1
A method of preparing a sample for in-situ observation by electron beam irradiation which observes an electric element having an electrolytic solution in an operating state, and preparing an electrode body in which a hole in the traveling direction of the electron beam is formed And preparing a counter electrode body configured to be capable of bringing the separator into contact with the electrode body at a contact position separated from the hole in a direction different from the traveling direction of the electron beam. And the electrolytic solution is attached to the electrode body so that the electrolytic solution is continued from the hole to the contact position, and the separator is brought into contact with the contact position. The method for producing a sample, wherein the electrode unit is brought into contact with the electrolytic solution through the separator.

  According to this application example, since the counter electrode body is brought into contact at a contact position separated from the hole of the electrode body in which the electrolytic solution is held in a direction different from the traveling direction of the electron beam, Observation is easier. In addition, since the electrode portion of the counter electrode body is in contact with the electrolytic solution continuous from the hole to the contact position via the separator, the sample can be operated as an electric element. Therefore, by observing the peripheral portion of the hole, it is possible to observe in situ the phenomenon that occurs in the vicinity of the interface between the electrode of the electric element in the operating state and the electrolytic solution.

Application Example 2
A method of producing a sample according to Application Example 1, wherein the hole is a through hole penetrating in the traveling direction of the electron beam.

  According to this application example, since the hole penetrates in the traveling direction of the electron beam, it is possible to observe the phenomenon occurring in the electrolytic solution held in the hole more clearly.

Application Example 3
It is a manufacturing method of a sample given in Application Example 1 or 2, wherein the electrode body has a thin section which can transmit the electron beam, and the hole is formed in the thin section. How to make

  According to this application example, by forming the holes in the thin section of a thickness that allows the transmission of the electron beam, it becomes easier to perform in-situ observation using a transmission electron microscope or a transmission scanning electron microscope. In addition, since the counter electrode body contacts the position separated from the thin plate portion in which the hole is formed in a direction different from the traveling direction of the electron beam, the risk of damaging the thin plate portion when contacting the counter electrode body is reduced. can do.

Application Example 4
A method for producing a sample according to Application Example 3, wherein the thin section is formed at one end of the electrode body, and the hole is formed near an end of the thin section. .

  According to this application example, by forming the thin section at one end of the electrode body and forming the hole in the vicinity of the end of the thin section, it is possible to more easily observe the peripheral portion of the hole by electron holography. .

Application Example 5
A method of producing a sample according to Application Example 4, wherein the plurality of holes are arranged obliquely to an end of the thin section.

  According to this application example, it is possible to more easily form an uncut edge capable of holding the electrolytic solution in the vicinity of the end of the thin section, which is easier to observe by electron holography. Therefore, it is possible to more easily prepare a sample suitable for observation by electron holography.

Application Example 6
In the method for producing a sample according to Application Example 4 or 5, a bulk piece made of a material constituting the electrode body is prepared, and a focused ion beam in the traveling direction of the electron beam is irradiated in the vicinity of the end of the bulk piece. Forming the holes, and irradiating the end of the bulk piece where the holes are formed with the focused ion beam in a direction different from the traveling direction of the electron beam, thereby forming the thin portion How to make a sample.

  In this application example, since the thin section is formed after the holes are formed, it is possible to suppress deformation of the thin section by the formation of the holes.

Application Example 7
A method for producing a sample according to application example 6, wherein prior to the formation of the hole, the end portion where the hole is formed is irradiated with a focused ion beam in a direction different from the traveling direction of the electron beam. A method of preparing a sample, which forms a thin portion of a thickness suitable for forming a hole.

  In this application, since the thin portion having a thickness suitable for forming the hole is formed, the hole can be formed more easily.

Application Example 8
It is a manufacturing method of a sample given in Application Example 6 or 7, wherein the bulk piece is made of carbon having a glassy structure.

  According to this application example, the phenomenon occurring at the interface between the carbon electrode and the electrolytic solution can be observed in situ. Further, by using carbon having a glassy structure, generation of noise derived from the crystal structure can be reduced, so that the phenomenon occurring at the interface between the carbon electrode and the electrolytic solution can be observed more clearly. It becomes possible.

Application Example 9
It is a manufacturing method of a sample given in application example 4, and it prepares porous powder which consists of the 1st material which constitutes the above-mentioned electrode body, and has pores, and constitutes particles of the above-mentioned porous powder in the above-mentioned electrode body. By fixing to one end of the support made of the second material and irradiating the particles of the porous powder fixed to the end of the support with a focused ion beam in a direction different from the traveling direction of the electron beam A method for producing a sample, wherein the thin section in which the hole is formed is formed.

  Generally, an electrode on which porous powder is fixed is used as an electrode of an electric element. Therefore, according to this application example, it is possible to observe the phenomenon occurring at the interface between the electrode and the electrolyte in a situation closer to that of an actual electric element.

Application Example 10
A method of producing a sample according to application example 9, wherein the porous powder is an activated carbon powder.

  According to this application example, the phenomenon occurring at the interface between the carbon electrode and the electrolytic solution can be observed in situ. Further, by using activated carbon powder, the generation of noise derived from the crystal structure can be reduced, so that the phenomenon occurring at the interface between the carbon electrode and the electrolytic solution can be observed more clearly.

Application Example 11
A method of producing a sample according to any of application examples 1 to 10, wherein the electrolytic solution is an ionic liquid.

  In general, ionic liquids have low vapor pressure and hardly evaporate even in vacuum. Therefore, in-situ observation can be performed using a general electron microscope in which the sample is placed in a vacuum.

Application Example 12
A method for in-situ observation of potential distribution in an operating state of an electric device having an electrolytic solution by electron holography, comprising: preparing a sample manufactured by the manufacturing method according to any one of application examples 4 to 10; A first electron beam hologram of the peripheral portion of the hole is acquired in a state where a voltage is applied between the electrode body and the counter electrode body, and a voltage is applied between the electrode body of the sample and the counter electrode body. The second electron beam hologram of the peripheral portion of the hole is obtained in a state where no voltage is applied, and from the first and second electron beam holograms, a phase shift method (for example, the method disclosed in Non-Patent Document 1) First and second reproduction phase images are respectively generated, and a differential phase image obtained by subtracting the second reproduction phase image from the first reproduction phase image is generated, and the electrode body and the counter electrode body are State of applying voltage between In, observing potential distribution at the peripheral portion of the hole, in situ observation method of potential distribution.

  In this application example, since a sample suitable for the observation by the electron holography of the peripheral portion of the hole is used, the electron beam hologram can be obtained more easily. Then, by generating a reproduced phase image by the phase shift method, a reproduced phase image and a differential phase image with high spatial resolution are generated, so that the potential distribution at the interface between the electrode and the electrolyte can be observed in more detail. It becomes possible.

  The present invention can be realized in various aspects. For example, the present invention can be realized in an aspect such as a sample preparation method and a sample observation method using the sample preparation method, an apparatus used in sample preparation, and an observation apparatus suitable for sample preparation.

Explanatory drawing which shows a mode that in-situ observation of the electric potential distribution in a sample is performed. Explanatory drawing which shows the electric double layer capacitor (EDLC) used as observation object of electric potential distribution, and distribution of the electric charge in EDLC, and an electric potential. The schematic diagram which shows the structure of the model sample of EDLC typically. Explanatory drawing which shows a mode that the model sample was attached to the sample holder. FIG. 5 is a process diagram showing a manufacturing process of an electrode body. Explanatory drawing which shows the electric charge distribution in the peripheral part of a through-hole, and the phase change amount of the electron beam at the time of permeate | transmitting the said peripheral part. The FIB image which image | photographed the front-end | tip part of the carbon piece which formed the through-hole using FIB. The TEM image of the through-hole part before and behind application | coating of an ionic liquid. Hologram and reproduction phase image of through-hole part. Differential phase image generated from the reconstructed phase image. The graph which shows the phase change amount profile calculated | required from the difference phase image. Process drawing which shows the process of producing the electrode body used in 2nd Embodiment. The TEM image which observed the front-end | tip part of the sample electrode which formed the thin part by FIB process. TEM image and electron beam hologram near the edge of thin section. Reconstructed phase image and differential phase image generated from the hologram of activated carbon particles. The graph which shows the phase change amount profile calculated | required from the differential phase image of FIG.

Embodiments of the present invention will be described in the following order.
A. First embodiment:
A1. In-situ observation of potential distribution:
A2. Observation target of potential distribution:
A3. Model sample:
A4. Preparation of electrode body:
A5. Observation of potential distribution in model sample:
A6. First embodiment:
B. Second embodiment:
B1. Preparation of electrode body and formation of model sample:
B2. Second embodiment:
C. Modification:

A. First embodiment:
A1. In-situ observation of potential distribution:
FIG. 1 is an explanatory view showing in-situ observation of potential distribution in a sample SPC. The potential distribution observation device 10 for performing in-situ observation of the potential distribution includes an electron holography microscope 100 and a DC power supply device 200. The sample SPC disposed inside the electron beam holographic microscope 100 and the DC power supply 200 having a variable output voltage are connected by two lead wires 12 and 14.

  The electron beam holography microscope 100 includes an electron beam irradiation device 110, an objective lens 120, and an electron beam biprism 130. The electron holography microscope 100 has an intermediate lens and a projection lens for enlarging and projecting an image formed on the image plane on the observation plane, and an imaging device for acquiring the image enlarged and projected on the observation plane. In FIG. 1, their illustration is omitted.

  The electron beam irradiation apparatus 110 has an electron source 112 and a focusing lens 114. The electron beam accelerated by the predetermined acceleration voltage and emitted from the electron source 112 becomes an approximately parallel electron beam by the focusing lens 114. The substantially parallel electron beam passes through the sample surface on which the sample SPC is disposed, and enters the objective lens 120. The electron beam entering the objective lens 120 is once converged and then enters the electron biprism 130.

  As shown in FIG. 1, the sample SPC is disposed in an observation area AO of approximately half of the sample surface. In the observation area AO in which the sample SPC is disposed, the incident electron beam interacts with the sample SPC to change the phase or amplitude of the electron beam (electron wave) as a wave. On the other hand, the electron beam that has passed through the area (vacuum area) AV where the sample SPC is not disposed in the sample surface has no interaction with the sample SPC, so the phase and amplitude of the electron wave do not change. In general, an electron wave that has passed through the observation area AO is called an object wave o, and an electron wave that has passed through the vacuum area AV is called a reference wave r.

  The electron biprism 130 is composed of a conductive filament 132 and a pair of ground electrodes 134 sandwiching the filament 132. A positive voltage is applied to the filament 132 with respect to the ground electrode 134. Although the ground electrode 134 is drawn as a parallel flat plate in FIG. 1, the shape of the ground electrode 134 is not limited to this. In general, the ground electrode 134 can have various shapes as long as the side facing the filament 132 is flat.

  By applying a positive voltage to the filament 132, an electron beam having a negative charge is attracted to the filament 132. Thereby, the electron beam which has passed through the sample surface and entered the electron biprism 130 is divided into the object wave Ψo and the reference wave Ψr. The divided object wave Ψ o and the reference wave よ う r are refracted so as to be superimposed on each other, and the object wave Ψ o and the reference wave Ψ r are superimposed. In the first embodiment, a positive voltage is applied to the filament 132 to the ground electrode 134 in order to superimpose the object wave o and the reference wave r, but depending on the configuration of the electron beam optical system, the object may be an object. A negative voltage is applied to the filament 132 with respect to the ground electrode 134 in order to overlap the wave o and the reference wave r.

  At this time, if the electron beam emitted from the electron source 112 is coherent, the object wave Ψo superimposed on the image plane and the reference wave Ψr interfere with each other to form an electron interference fringe IFF. As the coherent electron source, for example, it is possible to use a field emission type electron gun. The form of the interference fringes IFF formed in this way changes as the phase difference between the object wave Ψ o and the reference wave Ψ r changes. Therefore, when an electron beam interacts with an electric field, a magnetic field, or the like on the sample surface to change the phase of the object wave Ψo, distortion occurs in the interference fringe IFF. Therefore, by analyzing the distortion of the interference fringes, it is possible to reproduce the phase of the object wave Ψo and visualize the state of the electric field or the magnetic field that causes a phase difference. In addition, when the electron beam is blocked by the sample SPC and the amplitude of the object wave o decreases, an image ISP of the sample SPC is formed on the image plane.

  The process of analyzing the distortion of the interference fringes and reproducing the phase of the object wave Ψ o is performed on the interference fringes obtained by enlarging and projecting the interference fringes IFF formed on the image plane on the observation plane. Specifically, the interference fringes IFF formed on the image plane are enlarged and projected on the observation surface by an intermediate lens and a projection lens (neither of which is shown). The interference fringes enlarged and projected on the observation surface are acquired by an imaging device (not shown) such as a charge coupled device (CCD) provided on the observation surface. The phase of the object wave Ψo can be reproduced by analyzing the interference fringes obtained by the imaging device using a computer or the like. The reproduction of the phase from the interference fringes can be performed using various phase reproduction methods such as a phase shift method (see, for example, Non-Patent Document 1). Thus, by using the technique (electron holography) of reproducing the phase of the object wave o from the interference fringe IFF (electron beam hologram) obtained by causing the object wave o and the reference wave r to interfere with each other, Potential distribution can be observed. When the phase shift method is used as the phase reproduction method, the spatial resolution of the reproduced phase image can be increased to about 0.5 nm. Therefore, in the first embodiment, the phase shift method is used to reproduce the phase.

A2. Observation target of potential distribution:
FIG. 2 is an explanatory view showing an electric double-layer capacitor (EDLC: Electric Double-Layer Capacitor) 300 which is an observation target of the potential distribution, and the distribution of charge and potential in the EDLC 300. FIG. 2A is a schematic view showing a state in which a voltage is applied to the EDLC 300. As shown in FIG. The EDLC 300 includes an opposing collector electrode 312, 322, activated carbon electrodes 314, 324 disposed on the respective collector electrodes 312, 322, a separator 330, and an electrolytic solution 340 filled between the two collector electrodes 312, 322. And.

  The collector electrode 312 and the activated carbon electrode 314 constitute a first electrode 310 of the EDLC 300, and the collector electrode 322 and the activated carbon electrode 324 constitute a second electrode 320 of the EDLC 300. The separator 330 electrically isolates the two electrodes 310 and 320 and transmits ions in the electrolytic solution 340 to ensure ion conductivity between the two electrodes 310 and 320.

  As shown in FIG. 2A, the activated carbon electrodes 314 and 324 are composed of a large number of activated carbon particles 360. The activated carbon particles 360 themselves also have a large number of pores (not shown). Therefore, when the electrolytic solution 340 is filled between the two collector electrodes 312 and 322, the electrolytic solution 340 enters the voids between the activated carbon particles 360 and the pores of the activated carbon particles 360. Thereby, the area of the contact interface between the electrodes 310 and 320 and the electrolytic solution 340 is increased.

  In the example of FIG. 2A, the positive electrode of the DC power supply PS is connected to the first electrode 310, and the negative electrode of the DC power supply PS is connected to the second electrode 320. In this way, when a voltage is applied between the first electrode 310 and the second electrode 320, an electric double layer (described later) is formed at the wide interface between the electrodes 310 and 320 and the electrolyte 340. The electric double layer formed at the interface between the electrodes 310 and 320 and the electrolytic solution 340 has a function of storing charge, so the EDLC 300 functions as a large capacity capacitor.

  FIG. 2 (b) is a schematic view showing the distribution of the charge between the activated carbon particles 360 in the region shown by the broken line in FIG. 2 (a). As shown in FIG. 2A, a voltage is applied so that the first electrode 310 (hereinafter also referred to as “positive electrode”) side is positive and the second electrode 320 (hereinafter also referred to as “negative electrode”) side is negative. Is applied, as shown in FIG. 2B, in the activated carbon particles 360 constituting the positive electrode 310, positive charges gather in the vicinity of the interface with the electrolytic solution 340. On the other hand, in the electrolyte solution 340, anions having a negative charge gather in the vicinity of the interface with the activated carbon particles 360 constituting the positive electrode 310. Thus, a layer (electric double layer) in which positive and negative charges are arranged in pairs is formed at the interface between the activated carbon particles 360 of the positive electrode 310 and the electrolytic solution 340, and the positive and negative charges are accumulated. In addition, although a mode that an electric double layer is formed in the interface of the two activated carbon particles 360 which comprise the positive electrode 310, and the electrolyte solution 340 is shown in FIG.2 (b), an electric double layer is both electrodes The contact interfaces are formed at all contact interfaces with the electrolyte 310 and between the electrodes 310 and 320.

  FIG.2 (c) is a graph which shows the electric potential distribution between the activated carbon particle 360 shown in FIG.2 (b). The horizontal axis of FIG. 2 (c) represents the position in the left-right direction in FIG. 2 (b). Moreover, the vertical axis | shaft of FIG.2 (c) represents the electric potential in each position in arbitrary units (AU). At the position corresponding to the activated carbon particle 360 (activated carbon portion), since the activated carbon particle 360 has conductivity, the potential becomes a constant value according to the voltage applied between both electrodes 310 and 320. Then, at a position (electrolyte solution portion) corresponding to the electrolyte solution 340, the potential decreases from the interface with the activated carbon particles 360 toward the center according to the distribution of anions and cations in the electrolyte solution 340. Specifically, as shown in FIG. 2 (b), the potential drops rapidly near the interface where the anions are concentrated, and then asymptotically approaches zero potential (the first and second electrodes 310 as they move away from the interface). , 320)). In the first embodiment, such a spatial change in potential of the electrolyte portion, that is, the potential distribution is observed by electron holography using a model sample (described later) corresponding to the EDLC 300.

A3. Model sample:
FIG. 3 is a schematic view schematically showing the configuration of the model sample 900 of the EDLC 300 (FIG. 2). The model sample 900 includes an electrode body 910, an ionic liquid 940 applied to the electrode body 910, a separator 930, an activated carbon electrode 924, and an electrode plate 922. The electrode plate 922 is a narrow plate made of metal such as copper, and the activated carbon electrode 924 and the separator 930 are attached to the surface on the electrode body 910 side in this order. The activated carbon electrode 924 corresponds to the electrode portion in the present invention, and the whole of the activated carbon electrode 924 and the separator 930 corresponds to the counter electrode body in the present invention.

  The ionic liquid applied to the electrode body 910 is a salt of a liquid at about normal temperature in which at least one of the anion and the cation is an organic compound, and functions as an electrolytic solution. Generally, when observing the potential distribution, the model sample 900 is placed inside the high vacuum electron holographic microscope 100. At this time, if an electrolytic solution in which the electrolyte is dissolved in a solvent such as water is used as the electrolytic solution, the solvent is evaporated, the function as the electrolytic solution is lost, and the inside of the electron beam holography microscope 100 may be contaminated. Therefore, in the first embodiment, an ionic liquid which has an extremely low vapor pressure and hardly evaporates in vacuum is used as the electrolytic solution. As such an ionic liquid, various ionic liquids of ammonium type, imidazolium type, choline type, sulfonium type, pyrazolium type, pyridinium type, pyrrolidinium type or phosphonium type can be used. However, when observing the potential distribution, since the region to which the ionic liquid is applied is irradiated with the electron beam, it is preferable to use a pyrrolidinium-based ionic liquid having high reduction resistance.

  The electrode body 910 is manufactured by processing carbon (glassy carbon) having a glassy structure using a focused ion beam (FIB: Focused Ion Beam) in which ions such as gallium are finely narrowed (focused ion beam method) . A specific method of producing the electrode body 910 will be described later. The electrode body 910 made of glassy carbon has a bulk portion 912 having a large thickness and a thin portion 914 having a thickness (for example, 100 nm) through which an electron beam can be transmitted. A plurality of through holes 916 penetrating in the traveling direction of the electron beam in the electron holography microscope 100 (FIG. 1) (hereinafter, referred to as “electron beam traveling direction”) are provided at the tip of the thin section 914. Since the through holes 916 penetrate in the electron beam traveling direction, the through holes 916 can be referred to as holes in the electron beam traveling direction.

  As shown in FIG. 3, when an appropriate amount of ionic liquid 940 is applied to the tip of the electrode body 910, the ionic liquid 940 is held in the through holes 916 by surface tension. Thus, when the separator 930 is brought into contact with the portion of the bulk portion 912 to which the ionic liquid 940 is applied while the ionic liquid 940 is held in the through holes 916, the model sample 900 corresponding to the EDLC 300 (FIG. 2) It is formed.

  FIG. 4 is an explanatory view showing the model sample 900 (FIG. 3) attached to the sample holder 700. As shown in FIG. Here, the sample holder 700 is a mechanism for holding the sample SPC (that is, the model sample 900) on the sample surface of the electron holography microscope 100 (FIG. 1). Note that, for convenience of illustration, in FIG. 4, the sample attachment portion to which the sample SPC is attached in the sample holder 700 is enlarged and illustrated. When the sample holder 700 is attached to the electron holography microscope 100, the electron beam travels from the front side to the back side of the paper surface.

  The sample holder 700 has an outer frame 710, insulating plates 722, 732 fixed to the outer frame 710, fixing plates 724, 734 formed of metal such as copper, and set screws 728, 738. . The fixing plates 724 and 734 are provided with holes 726 and 736, respectively. Fixing plates 724, 734 are fixed to sample holder 700 by tightening set screws 728, 738 through holes 726, 736. Fixing plates 724 and 734 are connected to DC power supply 200 (FIG. 1) through separate lead wires (not shown), respectively, and it becomes possible to apply a voltage between fixing plates 724 and 734. ing.

  The electrode body 910 is attached to a support plate 740 formed of a metal such as copper using a conductive tape, a conductive paste, or the like. The electrode body 910 is fixed to the sample holder 700 by sandwiching the support plate 740 to which the electrode body 910 is attached between the fixing plate 724 and the insulating plate 722. An ionic liquid 940 is applied to the tip of the fixed electrode body 910, as shown in FIG. After application of the ionic liquid 940, the tip of the electrode plate 922 is adjusted to be positioned at the portion of the bulk portion 912 where the ionic liquid 940 is applied, and the electrode plate 922 is placed between the fixing plate 734 and the insulating plate 732. Pinch. Thereby, the separator 930 (FIG. 3) attached to the electrode plate 922 is in contact with the ionic liquid 940, and the model sample 900 is formed.

A4. Preparation of electrode body:
FIG. 5 is a process diagram showing a manufacturing process of the electrode body 910. As shown in FIG. In the manufacturing process of the electrode body 910, first, a bulk piece 910a of glassy carbon is prepared (FIG. 5 (a)). Here, the bulk piece 910a refers to a small piece of glassy carbon having a size (for example, a width and a length of 2 to 5 mm, and a thickness of 1 to 2 mm) sufficient for mechanical handling. The bulk piece 910a can be obtained, for example, by breaking a glassy carbon member larger than the bulk piece 910a. Alternatively, the bulk piece 910 a may be cut out of the glassy carbon member by various processing methods such as dicing. The obtained bulk piece 910a is attached to the sample holder 700 via the support plate 740, as shown in FIG.

  After the bulk piece 910a is attached to the sample holder 700, thinning of the tip of the bulk piece 910a is performed. Specifically, as shown in FIG. 5 (b), the tip of the bulk piece 910a (FIG. 5 (a)) is irradiated with FIB in a direction perpendicular to the direction of travel of the electron beam to form a through hole 916c (figure A thin portion 914b of a thickness (e.g., 0.5 to 2 [mu] m) suitable for the formation of 5 (c) is formed. As a result, a bulk piece 910 b having a thin portion 914 b and a bulk portion 912 is obtained.

  Then, a through hole 916c penetrating in the direction of electron beam travel is formed in the thin portion 914b. Specifically, as shown in FIG. 5C, the through hole 916c is formed by irradiating FIB in the electron beam traveling direction in the vicinity of the end (edge) of the thin portion 914b (FIG. 5B). Do. Thereby, the bulk piece 910c which has the thin part 914c in which the through-hole 916c was formed, and the bulk part 912 is obtained.

  The thin portion 914c in which the through hole 916c is formed is thinned to a thickness that allows transmission of the electron beam. Specifically, as shown in FIG. 5D, the thin section 914 is formed by irradiating the FIB in the direction orthogonal to the electron beam traveling direction. As a result, an electrode body 910 having a thin section 914 in which the electron beam can be transmitted and in which the through holes 916 are formed and a bulk section 912 is obtained. As described above, in the first embodiment, the thin portion 914c in which the through hole 916c is formed is thinned to form the thin portion 914. As described above, by performing the thinning after forming the through holes 916 c, it is possible to suppress the deformation of the thinned portion due to the formation of the through holes 916.

A5. Observation of potential distribution in model sample:
FIG. 6 is a cross-sectional view of the peripheral portion of the through hole 916, and is an explanatory view showing the charge distribution and the amount of phase change of the electron beam when passing through the peripheral portion. 6 (a) and 6 (b) show the charge distribution and the amount of phase change of the electron beam in the state where no voltage is applied between the electrode body 910 (FIG. 3) and the electrode plate 922, respectively. Is shown. As shown in FIG. 6A, the ionic liquid 940 applied to the electrode body 910 has a substantially uniform thickness in the thin section 914 outside the through hole 916. On the other hand, inside the through hole 916, the thickness of the ionic liquid 940 decreases inward from the edge (through hole edge) of the through hole 916. Then, as the distance from the through hole edge becomes longer, the thickness of the ionic liquid 940 becomes substantially uniform. In the region where the thickness is substantially uniform, the thickness of the ionic liquid 940 is approximately the same as the thickness of the thin portion 914.

  When no voltage is applied, the free electrons in the thin section 914 and the ions in the ionic liquid 940 are uniformly distributed in the interior, and all areas of the thin section 914 and the ionic liquid 940 are electrically It becomes neutral. Therefore, the amount of phase change of the electron beam is observed as the sum of only the amount of phase change due to the internal potential of the transmitting material. Specifically, as shown in FIG. 6B, the amount of phase change of the electron beam transmitted through the thin part 914 is the amount of phase change due to the internal potential of the thin part 914 itself hatched in the direction from the upper right to the lower left. And the amount of change in phase due to the internal potential of the ionic liquid 940 covering the thin section 914 hatched in the direction from the upper left to the lower right. As described above, in the thin section 914 outside the through hole 916, the ionic liquid 940 covers the electrode material with a substantially uniform thickness. Therefore, the amount of phase change due to the ionic liquid 940 covering the thin portion 914 has a substantially constant value. On the other hand, inside the through hole 916, the amount of phase change due to the ionic liquid 940 changes as the thickness of the ionic liquid 940 changes.

  6 (c) and 6 (d) show the charge distribution and the amount of phase change of the electron beam in the state where a voltage is applied between the electrode body 910 (FIG. 3) and the electrode plate 922, respectively. ing. As shown in FIG. 6C, the form of the ionic liquid 940 hardly changes even when a voltage is applied. However, in the thin section 914, a positive charge is collected at the interface with the ionic liquid 940, and in the ionic liquid 940, an anion is collected at the interface with the thin section 914 to form an electric double layer.

  Thus, when a voltage is applied, the potentials in the thin section 914 itself and the ionic liquid 940 covering the thin section 914 become higher than in the case where no voltage is applied. Therefore, as shown in FIG. 6D, the amount of phase change of the electron beam transmitted through the thin portion 914 is increased by the amount of phase change due to the voltage application hatched in the left and right direction. On the other hand, inside the through hole 916, the potential in the ionic liquid 940 decreases inward from the edge of the through hole as shown in FIG. 2 (c). Therefore, the amount of phase change due to voltage application inside the through hole 916 hatched in the vertical direction in FIG. 6 (d) decreases rapidly in the region near the through hole edge according to the change in potential. Then, as it moves inward, it approaches asymptotically to zero.

  Thus, the potential distribution in the ionic liquid 940 due to the formation of the electric double layer is observed as a phase change amount due to voltage application inside the through hole 916. Therefore, the potential distribution in the ionic liquid 940 by the electric double layer is obtained by obtaining a difference obtained by subtracting the amount of phase change observed in the state without voltage application from the phase change amount observed in the state with voltage applied. It is possible to observe

A6. First embodiment:
[Preparation of electrode body]
In order to observe the potential distribution in the ionic liquid, a sample electrode (corresponding to the electrode body 910 in FIG. 3) constituting a model sample of the electric double layer capacitor was manufactured. Specifically, a glassy carbon plate material was broken to obtain small pieces of glassy carbon (hereinafter also referred to as "carbon small pieces") corresponding to the bulk pieces 910a of FIG. Thereafter, as described above, the tip portion of the obtained carbon piece was processed with FIB of gallium to form a thin portion provided with a through hole, thereby producing a sample electrode.

  FIG. 7 is an FIB image obtained by imaging the tip of a carbon piece having a through hole formed by scanning the FIB. FIG. 7 (a) is an FIB image obtained by imaging the entire tip portion of the carbon piece, and FIG. 7 (b) is an FIB image obtained by magnifying the formed portion of the through hole. In each of the FIB images in FIGS. 7A and 7B, as shown in FIG. 5D, the through holes are formed before thinning so that the electron beam can be transmitted (see FIG. The appearance of the tip portion (corresponding to the region including the thin portion 914c) in 5 (c) is shown.

  In the first embodiment, as shown in FIG. 5, the tip of the carbon piece (corresponding to the bulk piece 910a in FIG. 5A) is thinned before the through hole is formed. Therefore, as shown in FIG. 7A, a flat surface is formed at the tip of the carbon piece by thinning. Then, by processing the thinned tip portion with FIB, as shown in FIG. 7B, a through hole penetrating in the electron beam traveling direction is formed. After the FIB images of FIG. 7A and FIG. 7B were photographed, as shown by the arrows in FIG. 7A, the tip was irradiated with FIB to be sliced to obtain a sample electrode. In the first embodiment, as shown in FIG. 7B, the plurality of through holes are arranged obliquely to the end of the tip. In general, electron holography observation is difficult to perform at a position away from the end of the tip. Therefore, in the first embodiment, in order to more easily form through holes whose edges are not cut at a position closer to the end of the tip, the plurality of through holes are arranged obliquely to the end of the tip. However, a single through hole may be formed, and a plurality of through holes may be arranged parallel to the end of the tip.

[Application of ionic liquid]
After producing the sample electrode, the ionic liquid was applied to the tip of the sample electrode. In addition, as an ionic liquid to apply | coat, the ionic liquid of the pyrrolidinium type | system | group which makes 1-butyl- 1-methyl pyrrolidinium a cation, and makes a bis (trifluoromethyl sulfonyl) imide an anion was used.

  FIG. 8 is a transmission electron microscope image (TEM image) of the through hole portion before and after application of the ionic liquid. The TEM images of FIG. 8 (a) and FIG. 8 (b) show the state before application of the ionic liquid and after application of the ionic liquid, respectively. As shown in FIG. 8 (a), it was confirmed that the through holes whose edges were not cut were formed at the tip of the sample electrode even after thinning. Further, as shown in FIG. 8B, it was confirmed that the ionic liquid is held in the through hole by applying the ionic liquid to the tip of the sample electrode.

[Photograph of electron beam hologram and generation of reproduction phase image]
After the ionic liquid is applied to the tip of the sample electrode, as shown in FIG. 3, the ionic liquid 940 applied to the sample electrode (corresponding to the electrode body 910 in FIG. 3) A separator 930 attached to 922 was brought into contact to form a model sample. Then, while changing the voltage (applied voltage) applied between the sample electrode and the electrode plate 922, an electron beam hologram (hereinafter, also simply referred to as "hologram") of the through hole portion was photographed. In the first example, a voltage was applied so that the sample electrode side was positive and the electrode plate side was negative. Next, the photographed hologram was analyzed by a computer to generate a reproduction phase image.

  FIG. 9 shows a hologram and a reproduction phase image of the through hole portion. FIGS. 9A to 9C are holograms when the applied voltage is 0 V, 1.5 V and 2.5 V, respectively. FIGS. 9D to 9F are reproduction phase images when the applied voltage is 0 V, 1.5 V and 2.5 V, respectively. In the holograms of FIGS. 9A to 9C, the presence of a region in which the interference fringes are greatly distorted was confirmed on the outside of the through hole, that is, on the inner peripheral end of the sample electrode. This region is a Ga insertion portion in which gallium (Ga) used when processing the sample electrode has entered glassy carbon. In the Ga insertion part, the internal potential of the sample electrode changes due to the presence of gallium. Therefore, the amount of phase change of the electron beam transmitted through the Ga insertion portion is different from that of the region where gallium does not enter. The difference in the amount of phase change between such a Ga insertion part and the other area of the sample electrode was also confirmed in the reproduced phase images of FIGS. 9 (d) to 9 (f).

  On the other hand, in the portion of the ionic liquid inside the through hole, a large phase change as in the Ga insertion portion does not occur. Therefore, in the holograms of FIGS. 9A to 9C, it is not always easy to confirm the phase distribution of the ionic liquid portion as distortion of the interference fringes. However, in the reproduced phase images of FIGS. 9 (d) to 9 (f), the distribution of the amount of phase change inside the through hole could be clearly observed.

[Generation of differential phase image and observation of potential distribution]
As described above, the potential distribution in the ionic liquid by the electric double layer is obtained by subtracting the amount of phase change observed without applying a voltage from the amount of phase change observed with applying a voltage. By observation. Therefore, from the reproduced phase images when the applied voltage is 1.5 V and 2.5 V, that is, from the reproduced phase images shown in FIGS. 9E and 9F, the reproduced phase when the applied voltage is 0 V. A differential phase image is generated by subtracting the image (FIG. 9 (d)). In the following, a differential phase image obtained by subtracting the reproduced phase image when the applied voltage is 0 V from the reproduced phase image when the applied voltage is xV (x is an arbitrary real number) is xV and the applied voltage is xV. It is also called a differential phase image when

  FIG. 10 is a differential phase image generated from the reproduction phase image. FIGS. 10A and 10B are differential phase images when the applied voltage is 1.5 V and 2.5 V, respectively. As can be seen from FIGS. 10A and 10B, in the portion of the sample electrode, the amount of phase change when the applied voltage is 2.5 V is the amount of phase change when the applied voltage is 1.5 V. It is bigger than that. From this, it can be understood that a voltage is applied to the sample electrode. In addition, in either case of the applied voltage of 1.5 V or 2.5 V, the amount of phase change in the ionic liquid portion inside the through hole was large on the sample electrode side. The distribution of the amount of phase change corresponds to the potential distribution of the electric double layer formed at the interface between the sample electrode and the ionic liquid.

[Evaluation of phase change profile]
In order to evaluate the range in which the electric double layer affects the potential distribution, the phase variation profile corresponding to the potential distribution was evaluated. Specifically, in FIGS. 10A and 10B, the phase change amount profile in the inward direction (profile evaluation direction) from the edge of the through hole was determined for the area surrounded by the white frame.

  FIG. 11 is a graph showing a phase change amount profile obtained from the differential phase image. FIGS. 11A and 11B show phase change amount profiles when the applied voltage is 1.5 V and 2.5 V, respectively. In FIGS. 11A and 11B, the horizontal axis represents the distance from the through hole edge (unit: nm), and the vertical axis represents the amount of phase change (unit: rad).

  As can be seen from FIGS. 11A and 11B, when the applied voltage is increased, the absolute value of the amount of phase change is increased, but the form of the profile is hardly changed. And, even when the applied voltage is 1.5 V or 2.5 V, the phase change amount at a distance from the edge of the through hole, ie, at a distance of 180 nm from the interface between the electrode and the electrolytic solution (ionic liquid) Became almost 0 rad. This indicates that the spread range of the potential distribution by the electric double layer is 180 nm. From this, in the case of using the ionic liquid used in the first embodiment as an electrolytic solution in the electric double layer capacitor (EDLC 300 of FIG. 2), the gaps between the activated carbon particles 360 or the pores of the activated carbon particles 360 are It was found that when the radius was 180 nm or more, the capacitance was saturated. That is, it was found that it is preferable to increase the number of pores having a radius of 180 nm or less in order to increase the capacity of the electric double layer capacitor using the ionic liquid used in the first embodiment as an electrolytic solution.

  As described above, according to the first embodiment and the first example, the through hole 916 is provided at the tip of the thin part 914 formed in the electrode body 910, and the ionic liquid 940 is applied near the tip of the electrode body 910. doing. At this time, the ionic liquid 940 is held in the through hole 916 by the surface tension of the ionic liquid 940, and the ionic liquid 940 continues to the electrode from the through hole 916 to the position where the separator 930 contacts. It adheres to the body 910. Therefore, when the separator 930 is in contact with the electrode body 910, the activated carbon electrode 924 contacts the ionic liquid 940 through the separator 930. Thus, the model sample 900 functions as an electric double layer capacitor.

  Further, since the bulk portion 912 in contact with the separator 930 is at a position separated from the through hole 916 in the direction different from the electron beam traveling direction, observation of the peripheral portion of the through hole 916 can be more easily performed. Damage to the thin section 914 due to contact with the 930 can be suppressed. Furthermore, since the through hole 916 is formed at the end of the thin part 914 formed at one end of the electrode body 910, that is, near the end of the thin part 914, the peripheral part of the through hole 916 can be more easily It can be observed by electron holography. Then, the hologram of the peripheral portion of the through hole 916 is photographed, and the hologram is analyzed, whereby the potential distribution of the peripheral portion of the through hole 916 can be observed.

  Although the electrode body 910 is formed of glassy carbon in the first embodiment and the first example, it is also possible to form the electrode body using another conductive material such as metal. However, it is preferable to use glassy carbon in that generation of noise derived from the crystal structure can be reduced and the potential distribution in the region including the ionic liquid 940 can be observed more clearly.

  Furthermore, in the first embodiment and the first example, the through hole 916 is formed to observe the peripheral portion of the through hole 916, but the hole for observing the peripheral portion does not necessarily have to penetrate. However, it is preferable to form the through hole 916 and observe the peripheral portion of the through hole 916 in that the potential distribution in the inside of the hole can be observed more clearly.

B. Second embodiment:
In the second embodiment, an electrode body manufactured using activated carbon powder is used instead of the electrode body 910 manufactured from the bulky piece 910a of glassy carbon (FIG. 5) as a model sample used for observation of potential distribution. The second embodiment differs from the first embodiment in the points. The other points are the same as those of the first embodiment, and therefore, the descriptions of the same matters as the first embodiment will be omitted here.

B1. Preparation of electrode body and formation of model sample:
FIG. 12 is a process chart showing a process of manufacturing an electrode assembly 980 (FIG. 12 (d)) used in the second embodiment. In the preparation process of the electrode body 980, first, a support 982 for fixing particles (activated carbon particles) 984 of activated carbon powder is prepared. The support 982 is a rod-shaped metal piece. In FIG. 12A, the support 982 is drawn as having the same outer diameter up to the tip, but the shape of the support 982 is not limited to this as long as it can be attached to the sample holder 700.

  Next, activated carbon particles 984 are fixed to the prepared support 982 (FIG. 12 (b)). Specifically, after a conductive paste is added to the activated carbon powder, a mixture of the activated carbon powder and the conductive paste is applied to the tip of the support 982. The activated carbon particles 984 are thereby fixed to the surface of the support 982. In FIG. 12B, only the activated carbon particles 984 directly fixed to the support 982 are drawn for convenience of illustration, but in general, the support is in a state where a large number of activated carbon particles 984 are fixed to each other. It is fixed to 982. After the activated carbon particles 984 are fixed to the support 982, the portion of the support 982 to which the mixture of the activated carbon powder and the conductive paste is not applied is a fixing plate 724 and an insulating plate 722 of the sample holder 700 (FIG. 4). In between. Thereby, activated carbon particles 984 fixed to the support 982 and the support 982 are fixed to the sample holder 700.

  After the support 982 is fixed to the sample holder 700, the activated carbon particles 984 fixed to the tip of the support 982 are exfoliated (FIGS. 12 (c) and 12 (d)). Specifically, activated carbon particles 984 fixed to the front end of the support 982 are irradiated with FIB such as gallium to form activated carbon particles 984 c having one flat surface (FIG. 12C). Next, the activated carbon particles 984 c provided with the flat surface are further irradiated with FIB to form activated carbon particles 984 d having a flaky portion 986 (FIG. 12 (d)). As a result, an electrode body 980 whose tip is sliced is obtained. As described above, in FIGS. 12 (b) to 12 (d), only the activated carbon particles 984 directly fixed to the support 982 are drawn for convenience of illustration. Therefore, in FIG. 12C and FIG. 12D, although one activated carbon particle 984 is depicted as being exfoliated, generally, a plurality of activated carbon particles 984 fixed to the tip of the support 982 It is sliced.

  In order to form a model sample using the obtained electrode assembly 980, a sufficient amount of ionic liquid is first permeated into the portion (activated carbon fixation portion) to which the activated carbon particles 984 of the electrode assembly 980 are fixed. Thereby, an ionic liquid is hold | maintained at the pore (not shown) which the activated carbon particle 984 has. After permeating the ionic liquid into the activated carbon-fixed portion, the separator 930 attached to the electrode plate 922 via the activated carbon electrode 924 is brought into contact with the position separated from the flake portion 986 of the activated carbon-fixed portion as in the example of FIG. Let Specifically, similarly to the example of FIG. 4, the tip of the electrode plate 922 is adjusted to be positioned at the activated carbon fixing portion, and the electrode plate 922 is sandwiched between the fixing plate 734 and the insulating plate 732. As a result, the separator 930 attached to the electrode plate 922 comes in contact with the ionic liquid that has permeated the activated carbon fixing portion, and a model sample is formed.

B2. Second embodiment:
[Preparation of sample electrode]
In order to produce a sample electrode, first, a tungsten tip corresponding to a support 982 (FIG. 12) was prepared. Next, a mixture of activated carbon powder and conductive paste was applied to the tip of the prepared tungsten tip. Thereafter, as described above, the activated carbon particles fixed to the tip of the tungsten tip were exfoliated using FIB of gallium to obtain a sample electrode having the exfoliated part.

  FIG. 13 is a TEM image obtained by observing the tip of a sample electrode (corresponding to the electrode assembly 980 in FIG. 12D) in which a thin portion is formed by FIB processing. FIG. 13 (a) is a TEM image of the tip of the sample electrode observed at low magnification. As shown in FIG. 13 (a), a large number of activated carbon particles constituting the sample electrode and voids formed between the activated carbon particles were observed. FIG. 13 (b) is a medium magnification TEM image of the tip of the sample electrode. In the TEM image of FIG. 13 (b), a large number of pores possessed by the activated carbon particles could be confirmed. Further, as shown in FIG. 13B, the width of the region where the interference fringes are formed by the electron beam biprism 130 (FIG. 1) is about 300 nm on the sample surface. Therefore, the area where the hologram can be observed is a narrow range of about 300 nm from the tip of the thin section. The hologram can be performed by moving the electron biprism 130 in the direction of the sample electrode so that interference fringes are formed at the position of the sample electrode.

  FIG. 14 is a TEM image and a hologram near the end of the thin section. FIG. 14 (a) is a high-magnification TEM image of activated carbon particles near the end of the thin section. As shown in FIG. 14 (a), it was confirmed that pores of various sizes were formed in the activated carbon particles. FIG. 14 (b) is a hologram of activated carbon particles. As shown in FIG. 14 (b), the interference fringes of the hologram were slightly distorted in the portion (pore portion) where the pore is formed. The distortion of the interference fringes in the pore portion is considered to be because the thickness of carbon for changing the phase of the electron beam is thinner than the portion (matrix portion) of the matrix around the pore. As described above, since the pore portion is in a depressed state, that is, the surface of the pore portion is located on the electron beam traveling direction side with respect to the surface of the matrix portion, the pores of the activated carbon are , It can be called a hole in the electron beam traveling direction.

[Evaluation of potential distribution]
The potential distribution was evaluated by the electric double layer formed in the pores. Specifically, the same ionic liquid as in the first embodiment was allowed to permeate the activated carbon fixing portion of the sample electrode in which the thin portion was formed. Then, a separator 930 attached to the electrode plate 922 was brought into contact with the activated carbon fixing portion to which the ionic liquid was made to penetrate, through the activated carbon electrode 924 (FIG. 3), to form a model sample. After formation of the model sample, the hologram at the tip of the thin section was photographed while changing the applied voltage, and the photographed hologram was analyzed by a computer to generate a reproduced phase image and a differential phase image.

  FIG. 15 shows a reproduced phase image and a differential phase image generated from a hologram of activated carbon particles. FIGS. 15 (a) and 15 (b) are reproduction phase images when the applied voltage is 1.5 V and 2.5 V, respectively, and FIGS. 15 (c) and 15 (d) are respectively. It is a differential phase image when the applied voltage is 1.5V and 2.5V. As shown in FIGS. 15 (a) to 15 (d), vertical stripe noise appeared in the reproduced phase image and the differential phase image. The noise in the vertical stripes is an artifact caused by generating a reproduced phase image by the phase shift method, and it is not easy to remove. Therefore, phase change amount profiles were obtained for profile evaluation areas A-B along the vertical stripes, which are indicated by black frames in FIGS. 15 (c) and 15 (d).

  FIG. 16 is a graph showing a phase change amount profile obtained from the differential phase image of FIG. In FIG. 16A and FIG. 16B, the solid lines indicate phase change amount profiles when the applied voltage is 1.5 V and 2.5 V, respectively. 16 (a) and 16 (b), the horizontal axis represents the distance (in nm) from the end (end of the evaluation area) of the profile evaluation area, and the vertical axis represents the amount of phase change (in units). , Rad). Black circles in FIGS. 16A and 16B are obtained by superposing the phase change amount profiles obtained in the first embodiment. When the phase change amount profiles of the first embodiment and the second embodiment are superimposed, the position of the through hole edge in the first embodiment and the phase change amount at that position are the same as those of the pores in the second embodiment. The phase change amount profile of the first embodiment is shifted so as to correspond to the position of the edge and the phase change amount at that position.

  As can be seen from FIGS. 16 (a) and 16 (b), the shape of the phase variation profile inside the pores of the activated carbon was similar regardless of the level of the applied voltage. Also, it was found that the phase variation profiles of the first embodiment and the second embodiment in the inside of the hole closely match each other when the applied voltage is 1.5 V or 2.5 V. From this, it was found that it is possible to evaluate the potential distribution by the electric double layer formed in the pores of the activated carbon. Also, as in the first embodiment, an actual electric double layer capacitor (EDLC 300 in FIG. 2) is formed by forming a model sample using a sample electrode made of glassy carbon and having a thin plate portion in which through holes are formed. It has been found that it is possible to predict the potential distribution at a sufficiently high accuracy.

  As described above, according to the second embodiment and the second example, the flake portion 986 is formed at one end of the activated carbon fixing portion, and the sufficient amount of ionic liquid is allowed to permeate the activated carbon fixing portion. At this time, the ionic liquid is held in the pores derived from the activated carbon of the flake portion 986, and the electrode body 980 is continuous at least in the gaps in the activated carbon fixing portion from the pores to the position where the separator 930 contacts. Adhered to Therefore, when the separator 930 is in contact with the electrode body 980, the activated carbon electrode 924 contacts the ionic liquid through the separator 930. Thus, the model samples of the second embodiment and the second example function as an electric double layer capacitor.

  In addition, the contact position of the separator 930 is a position away from the thin plate portion 986 in the activated carbon fixing portion, that is, a position away from the activated carbon-derived pores of the thin portion 986 in a direction different from the electron beam traveling direction. Therefore, the peripheral portion of the pore can be more easily observed, and damage to the thin portion 986 due to the contact of the separator 930 can be suppressed. Furthermore, since the pores are ubiquitous throughout the flake portion 986, they also exist near the end of the flake portion 986. Therefore, the periphery of the pore can be observed by electron holography. Then, by taking a hologram of the pore periphery and analyzing the hologram, the potential distribution in the pore periphery can be observed.

  Further, according to the second embodiment and the second example, since the electrode body 980 is formed by fixing activated carbon powder, the configuration is similar to an electrode generally used in an electric double layer capacitor. Therefore, it is possible to observe the potential distribution in a situation closer to an actual electric double layer capacitor than in the first embodiment and the first example. On the other hand, in the first embodiment and the first example, since the peripheral portion of the through hole 916 can be observed, the potential distribution in the inside of the hole, that is, in the ionic liquid can be observed more clearly. .

C. Modification:
The present invention is not limited to the above-described embodiments and examples, and can be implemented in various modes without departing from the scope of the present invention. For example, the following modifications are possible.

C1. Modification 1:
In each of the above embodiments and examples, in order to perform observation using the electron holography microscope 100 in which the sample SPC is placed in a vacuum, an ionic liquid that hardly evaporates in vacuum is used as the electrolyte. However, as in Patent Document 2, when the sample can be observed in a specific gas atmosphere, an electrolyte solution in which an electrolyte is dissolved in a solvent can also be used as the electrolyte.

C2. Modification 2:
In each of the above embodiments and examples, although the target of in-situ observation is an electric double layer capacitor, the present invention is applied to in-situ observation of various electric elements such as primary batteries and secondary batteries having an electrolytic solution. be able to. In this case, the electrode body is formed by using a bulk piece or porous powder of an electrode material used in an observation target in place of glassy carbon or activated carbon powder. The bulk pieces and the porous powder are preferably amorphous in that generation of noise derived from the crystal structure can be reduced.

C3. Modification 3:
Although the present invention is applied to the observation of the potential distribution in the electrolytic solution of the electric double layer capacitor in each of the above-described embodiments and examples, the present invention relates to structural changes such as generation of dendrite in a lithium battery. It is possible to apply also at the time of field observation. In the case of observing the structural change in situ, the image ISP of the sample SPC (FIG. 1) may be observed without using electron holography. In this case, in-situ observation can be performed by a general transmission electron microscope. When electron holography is not used, it is also possible to form a thin section at an arbitrary position of the electrode body, such as the central part of the electrode body, and to form holes at any positions of the thin section. It is also possible.

C4. Modification 4:
In each of the above embodiments, examples and modifications, the present invention is applied to preparation of a sample for performing in-situ observation with a transmission electron microscope, but the present invention is not limited to transmission electron microscopy, and transmission scanning It can apply to preparation of the sample for performing in-situ observation by various electron microscopes, such as a type electron microscope and a scanning electron microscope. In the case where it is not necessary to transmit an electron beam as in a scanning electron microscope, the formation of the thin section can be omitted.

DESCRIPTION OF SYMBOLS 10 ... Potential distribution observation apparatus 12, 14 ... Lead wire 100 ... Electron beam holography microscope 110 ... Electron beam irradiation apparatus 112 ... Electron source 114 ... Focusing lens 120 ... Objective lens 130 ... Electron beam biprism 132 ... Filament 134 ... Grounding electrode 200 ... DC power supply 310, 320 ... electrode 312, 322 ... collector electrode 314, 324 ... activated carbon electrode 330 ... separator 340 ... electrolyte solution 360 ... activated carbon particles 700 ... sample holder 710 ... outer frame 722 732 ... insulating plate 724, 734 ... Fixing plate 726, 736: Hole 728, 738: Fixing screw 740: Support plate 900: Model sample 910: Electrode body 910a, 910b, 910c: Bulk piece 912: Bulk portion 914: Thin portion 914b, 914c: Thin portion 916, 916c ... through hole 922 ... electrode plate 92 ... Activated carbon electrode 930 ... Separator 940 ... Ionic liquid 980 ... Electrode body 982 ... Support 984 984 c, 984 d ... Activated carbon particle 986 ... Thin section AO ... Observation area AV ... Vacuum area IFF ... Interference fringes ISP ... Image PS ... DC power supply SPC ... sample Ψ o ... object wave Ψ r ... reference wave

Claims (12)

A method of preparing a sample for in-situ observation by electron beam irradiation in which an electric element having an electrolytic solution is observed in an operating state,
Preparing an electrode body having a thin section capable of transmitting the electron beam and having a hole in the traveling direction of the electron beam formed in the thin section ;
A counter electrode body comprising an electrode portion and a separator, wherein the separator can be brought into contact with the electrode body at a contact position separated from the hole in a direction different from the traveling direction of the electron beam Prepare
The electrolytic solution is adhered to the electrode body so that the electrolytic solution is held in the hole and the electrolytic solution is continuous from the hole to the contact position,
By bringing the separator into contact with the contact position, the electrode portion is brought into contact with the electrolytic solution via the separator.
How to make a sample. A method for producing a sample according to claim 1, wherein
The hole is a through hole that penetrates in the traveling direction of the electron beam.
How to make a sample. The method for producing a sample according to claim 1 or 2 , wherein
The thin section is formed at one end of the electrode body,
The hole is formed in the vicinity of the end of the thin section.
How to make a sample. A method for producing a sample according to claim 3 , wherein
A plurality of the holes are arranged obliquely to the end of the thin section;
How to make a sample. A method of producing a sample according to claim 3 or 4 , wherein
Preparing a bulk piece made of a material constituting the electrode body,
The hole is formed by irradiating a focused ion beam in the traveling direction of the electron beam in the vicinity of the end of the bulk piece;
The thin section is formed by irradiating a focused ion beam in a direction different from the traveling direction of the electron beam at the end of the bulk piece where the hole is formed.
How to make a sample. A method for producing a sample according to claim 5 , wherein
Prior to the formation of the hole, a thin portion with a thickness suitable for the formation of the hole is formed by irradiating the end where the hole is formed with a focused ion beam in a direction different from the traveling direction of the electron beam. Do,
How to make a sample. A method of producing a sample according to claim 5 or 6 , wherein
The bulk piece is made of carbon having a glassy structure,
How to make a sample. A method for producing a sample according to claim 3 , wherein
Preparing a porous powder having pores and made of a first material constituting the electrode body,
The particles of the porous powder are fixed to one end of a support made of a second material constituting the electrode body,
The thin particle portion in which the holes are formed is formed by irradiating the particles of the porous powder fixed to the end of the support with a focused ion beam in a direction different from the traveling direction of the electron beam.
How to make a sample. A method for producing a sample according to claim 8 , wherein
The porous powder is activated carbon powder,
How to make a sample. The method for producing a sample according to any one of claims 1 to 9 , wherein
The electrolyte is an ionic liquid,
How to make a sample. An in-situ observation method of potential distribution in an operating state of an electric element having an electrolytic solution by electron holography,
A sample prepared by the preparation method according to any one of claims 3 to 9 is prepared,
Acquiring a first electron beam hologram of a peripheral portion of the hole in a state where a voltage is applied between the electrode body of the sample and the counter electrode body;
Acquiring a second electron beam hologram of the peripheral portion of the hole in a state where a voltage is not applied between the electrode body of the sample and the counter electrode body;
First and second reproduction phase images are generated from the first and second electron beam holograms by phase shift method,
A peripheral portion of the hole in a state where a differential phase image is generated by subtracting the second reproduction phase image from the first reproduction phase image, and a voltage is applied between the electrode body and the counter electrode body. Observe the potential distribution at
In-situ observation method of potential distribution. The in-situ observation method of the electric potential distribution according to claim 11 .
The electrolyte is an ionic liquid,
In-situ observation method of potential distribution.