JP7565573B2 - Sample assembly, device for observing gas to be observed, and method for observing ions to be observed - Google Patents

Description

The present invention relates to a sample conjugate for contacting a target gas with the back surface of a sample, exciting the target gas such as hydrogen that is generated on the surface of the sample with an electron beam, and observing the target ions that are desorbed from the surface, as well as an observation device for the target gas using the sample conjugate and a method for observing the target ions using the sample conjugate.

Electron stimulated desorption (ESD) is a method of surface analysis in which adatoms are ionized and desorbed by irradiation with electrons, and is a well-known technique in the field of surface analysis. Using the ESD method, it is possible to directly observe target gases such as hydrogen in real time (see Non-Patent Documents 1 and 2).

For example, if the gas being observed is hydrogen, the ESD method can be used to visualize the positional information of hydrogen residing on the surface. However, once all the hydrogen has been desorbed, measurement cannot be continued, so this method is not suitable for measuring the amount of hydrogen that escapes from the steel, which exists in minute amounts.

The inventors have developed a hydrogen permeation diffusion path observation device that consists of a collection mechanism with a high hydrogen ion yield rate and an ion energy decomposition section that selectively allows hydrogen ions to pass through, and a method for measuring hydrogen ions passing through a sample using the device, when hydrogen is introduced into the sample from the back side and hydrogen atoms that diffuse through the sample and pass (emerge) to the front side are obtained by the ESD method (see Patent Documents 1 and 2).

The hydrogen permeation diffusion path observation device is a type of operando hydrogen microscope that excites hydrogen that has escaped from a sample with the scanning electrons of an electron microscope, desorbs it, and images it. An operando hydrogen microscope is an observation device that allows hydrogen to permeate a material and captures the released portion as a two-dimensional image. In conventional operando hydrogen microscopes, the observation sample is fixed at the partition of the vacuum vessel, and the low vacuum side of the sample is exposed to hydrogen gas at an appropriate partial pressure, allowing hydrogen that has diffused into the solid to be observed as escaped hydrogen on the high vacuum side.

Hydrogen embrittlement in structural materials is a major problem, and is a research field that will become more important as hydrogen utilization in society progresses. Hydrogen embrittlement is believed to be caused by hydrogen from corrosion, welding, pickling, electroplating, etc. This type of hydrogen-induced destruction is called "delayed destruction." Hydrogen embrittlement destruction is said to be likely to occur at grain boundaries, points where tensile stress is applied, and areas where stress is concentrated.
There has been a long history of research into hydrogen embrittlement, and much research is still being done today. Many of the research topics on hydrogen materials and hydrogen embrittlement are aimed at the behavior of hydrogen when structural materials are subjected to strain or stress. However, the factors that cause embrittlement are intricately intertwined with many factors including materials, structures, stress, and the environment, and the essence of the phenomenon is still unknown.

JP 2017-187457 A JP 2019-145255 A

Akiko Itakura, Yoshiharu Murase, Masahiro Tosa, Shinji Suzuki, Shoji Takagi, Tetsuji Goto, "Effect of surface treatment of stainless steel on hydrogen release," J. Vac. Soc. Jpn., Vol. 57, No. 1, pp. 23-26, 2014 Naoya Miyauchi, Shinji Suzuki, Shoji Takagi, Tetsuji Goto, Yoshiharu Murase, Akiko Itakura, "Observation of hydrogen permeation distribution on stainless steel surface," J. Vac. Soc. Jpn., Vol. 58, No. 10, pp. 31-35, 2015

Distortion and stress affect the permeability of various gases including hydrogen, and it is predicted that hydrogen will localize at the points of stress and strain, causing hydrogen embrittlement. For this reason, it is desirable to observe target gases such as hydrogen in a state where various stresses, which are influencing factors, are induced in the sample. However, it is not desirable to generate stress by contacting the observation area, such as by using an indenter to push up the observation area of the sample.

The present invention aims to provide a sample assembly that can generate a desired stress in the observation area of the sample without contact, without pushing up the observation area of the sample with an indenter or the like, when observing the target ions generated by irradiating the front surface with an electron beam while the back surface is in contact with the target gas.

Another object of the present invention is to provide an observation device for a target gas and an observation method for a target ion, which can be used to observe the permeability characteristics of a target gas while generating a desired stress in a non-contact manner in the observation area of the sample, and which can be applied to exploring the mechanisms of embrittlement and deterioration phenomena of structural materials caused by a target gas containing hydrogen, such as hydrogen embrittlement.
That is, when performing gas permeation measurements of various target gases including hydrogen, the permeation characteristics change depending on whether or not stress is applied to the sample. Therefore, the present invention proposes a sample assembly that utilizes thermal stress to apply stress to the sample.

The sample bonded body of the present invention for achieving the above object includes a sample for ionizing an observation target gas that has been transmitted from the back side to the front side and observing the ions in an observation device, and an auxiliary plate arranged on the back side of the sample, the sample has an observation area set at the center of its front side, the auxiliary plate has a thermal expansion coefficient different from that of the sample, has an opening at a position corresponding to the observation area of the sample , has approximately the same outer shape as the sample, and is directly bonded to the sample in a laminated state without a stress relaxation layer around the entire periphery of the opening, the sample and the auxiliary plate are bonded at a bonding temperature different from the temperature during observation in the observation device, and is configured so that stress is applied to the observation area of the sample to observe the ions . The thickness of the observation area in the sample may be approximately the same as the size of the crystal grains of the sample. The thickness of the observation area may be 100 to 300 μm. The thickness of the auxiliary plate may be thicker than the sample.

In order to achieve the above object, the present invention provides an observation device for observing target ions in a target gas by mounting the above-mentioned sample assembly, the observation device comprising: a scanning electron microscope for detecting secondary electrons generated by irradiating an observation region of the sample with an electron beam in an analysis chamber; a vacuum vessel having a hollow portion into which a target gas is introduced and in which the sample assembly is mounted so as to separate the hollow portion from the analysis chamber by the sample; a temperature adjusting unit for adjusting the temperature of the sample assembly mounted in the vacuum vessel; and a target ion detecting unit capable of detecting target ions generated by bringing the target gas introduced into the hollow portion into contact with the back surface of the sample and irradiating an observation region on the front surface with an electron beam. The temperature adjusting unit preferably comprises a heating/cooling unit for heating and cooling the sample assembly mounted in the vacuum vessel, and a temperature control unit for controlling the heating/cooling unit to adjust the temperature of the sample assembly.

The method for observing target ions of the present invention for achieving the above-mentioned object is characterized in that, when measuring target ions using the above-mentioned sample conjugate, the sample conjugate is mounted in a vacuum container so as to separate a hollow portion from an analysis chamber by the sample, and is placed in an analysis chamber of a scanning electron microscope, the temperature of the sample conjugate is set to an observation temperature, and an observation target gas introduced into the hollow portion is brought into contact with the back surface of the sample, and an electron beam is irradiated onto an observation area on the front surface to detect the generated observation target ions.

According to the sample assembly of the present invention, by setting the observation temperature to be different from the temperature at which the sample and the auxiliary plate are joined, the sample and the auxiliary plate each thermally expand or contract, and stress due to the difference in thermal expansion coefficients is generated in the observation area of the sample placed in the opening of the auxiliary plate. This makes it possible to generate a desired stress by selecting a combination of materials for the sample and the auxiliary plate, selecting the shape, size, thickness, etc., and selecting the temperature at the time of joining and the temperature at the time of observation. Therefore, when observing the observation target ions generated by irradiating the surface of the sample with an electron beam while the back surface of the sample is in contact with the observation target gas, it is possible to provide a sample assembly that generates a desired stress in the observation area of the sample without contact, without pushing up the observation area of the sample with an indenter or the like.

According to the observation device for a target gas and the observation method for target ions of the present invention, a sample assembly is attached to a vacuum vessel so that the sample separates the hollow space from the analysis chamber, and the target gas introduced into the hollow space is brought into contact with the back surface of the observation area of the sample, and an electron beam is irradiated onto the observation area on the front surface to generate target ions, which can be detected by a target ion detection unit.
In this case, since a desired stress can be generated in the observation region of the sample by adjusting the temperature of the sample conjugate to a desired temperature by the temperature adjusting unit, it is possible to detect the observation target ions in a state where a desired stress is generated in the observation region of the sample without contact using the sample conjugate. Therefore, it is possible to provide an observation device for an observation target gas and an observation method for an observation target ion suitable for observing the observation target gas using the sample conjugate.

1A is a perspective view of a sample bonded body according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of the sample bonded body. 5A to 5C are diagrams illustrating a stress generating method according to an embodiment of the present invention. 1A to 1C are explanatory diagrams for performing stress calculations. 1 is a diagram showing a schematic configuration of an observation target gas permeation diffusion path observation device in an embodiment of the present invention. FIG. 2 is a partially enlarged view showing the structure of an observation target ion detection unit in an analysis chamber and the mounting structure of a vacuum vessel in an observation device for observing a permeation diffusion path of an observation target gas in an embodiment of the present invention. FIG. 1 is a cross-sectional view showing a schematic diagram of a diaphragm-type vacuum container according to an embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a control unit according to the embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of an overall electronic stimulated desorption control unit according to an embodiment of the present invention. 4 is a schematic diagram showing the relationship between scanning of an electron source and two-dimensional measurement of an ESD image according to an embodiment of the present invention. FIG. FIG. 1 is a flow diagram for measuring a two-dimensional ESD image by electron beam scanning according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a sample assembly according to an embodiment of the present invention. As shown in FIGS. 1(a) and 1(b), a sample assembly 17 is configured by laminating a sample 17b on an auxiliary plate 17a in a bonded state.

(Configuration of sample assembly 17)
The sample 17b is a sample for which various characteristics such as the transmission and diffusion path of the target gas are observed under a state in which stress or strain is generated, and the material may be either metal or nonmetal, and is not particularly limited. The shape may be appropriately selected, and may be a plate, a film, or the like. In this embodiment, the sample is formed in a circular film shape. In the present invention, one surface of the sample or sample assembly on which the target ions generated by irradiation with an electron beam are observed is referred to as the front surface or upper surface, and the other surface of the sample or sample assembly that brings the target gas into contact with the observation region is referred to as the back surface or lower surface, but it should be noted that the front and back surfaces or the top and bottom surfaces of the sample or sample assembly are relative concepts that differ depending on the structure of the device.
The sample 17b has an inner central position separated from the periphery set as an observation region 17d for observing target ions. The observation region 17d may have properties different from those of the periphery, but in this embodiment, the entire observation region 17d is formed to have approximately the same thickness. For example, in the case of a metal sample 17b, the thickness of the observation region 17d in the sample 17b of the sample assembly 17 arranged as a diaphragm may be approximately the same as the size of the crystal grains of the sample, for example, about 100 to 300 μm.

The auxiliary plate 17a is a plate made of a material having a different thermal expansion coefficient from that of the sample 17b. The shape can be appropriately selected within a range in which the observation area 17d of the sample 17b can be appropriately positioned when the auxiliary plate 17a is attached to the observation device. In this embodiment, the auxiliary plate 17a is formed in a ring shape with a circular opening (hole) 17c provided in the central position corresponding to the observation area 17d of the sample 17b, and the outer shape of the auxiliary plate 17a and the outer shape of the sample 17b are formed to be approximately the same shape. The thickness of the auxiliary plate 17a is made sufficiently thicker than the thickness of the sample 17b. By making the thickness of the auxiliary plate 17a thicker than that of the sample 17b, a large stress can be created in the sample 17b.

In FIG. 1, one surface of the auxiliary plate 17a (hereinafter referred to as the upper surface) is the surface to which the sample 17b is joined. The other surface of the auxiliary plate 17a, i.e., the lower surface, is mirror-polished to serve as a sealing surface that comes into close contact with the diaphragm-type vacuum vessel 12 described below. The auxiliary plate 17a only needs to have a thermal expansion coefficient different from that of the sample 17b, and examples of materials for the auxiliary plate 17a with low thermal expansion coefficients include silicon, invar, and super invar. Conversely, examples of materials with high thermal expansion coefficients include aluminum, acrylic, and bakelite.

The sample 17b and the auxiliary plate 17a are directly laminated and bonded on their opposing surfaces without any intervening stress relaxation layer. The stress relaxation layer is a layer that makes it difficult for relative displacement to occur between the sample 17b and the auxiliary plate 17a at the bonded portion when the sample 17b and the auxiliary plate 17a thermally expand in the bonded state, that is, a layer that relaxes the relative displacement, and is not formed in this embodiment.
The sample 17b and the auxiliary plate 17a are bonded at a temperature different from that during the observation. Therefore, by making the temperature of the sample assembly 17 different from that during the bonding, stress is generated due to the difference in the thermal expansion coefficient. In this embodiment, stress is generated in the sample 17b due to the difference in the thermal expansion coefficient, and the behavior of the target gas is observed in this state.
An opening 17c is formed in the center of the auxiliary plate 17a, and since only the sample 17b is contained in this opening 17c, by observing the transmission of the target gas through this portion, it is possible to observe the transmission of the target gas through the stressed sample 17b.

(Method of joining sample and auxiliary plate)
Regarding the method of joining the sample 17b and the auxiliary plate 17a, if both are metals, general metal joining methods such as welding and brazing can be used. On the other hand, if both are metal and non-metal, general ceramic sealing methods such as metallizing the non-metal surface, inserting a binder, and brazing after plating can be used. Even if both are non-metal and non-metal, general joining methods similar to the above-mentioned non-metal surface treatment can be used.
However, a bonding method that generates a stress relaxation layer between the sample 17b and the auxiliary plate 17a is not used because the stress generated in the sample 17b is reduced if a stress relaxation layer having a lower strength than the sample 17b and the auxiliary plate 17a is interposed between the sample 17b and the auxiliary plate 17a.

(How stress is generated)
In the sample assembly 17, the sample 17b and the auxiliary plate 17a are heated and/or cooled to change the temperature, thereby generating stress in the observation area 17d of the sample 17b.
First, when the thermal expansion coefficient of the sample 17b to be observed is the same as that of the auxiliary plate 17a, as shown in FIG. 2(a), even if the temperature of the sample assembly 17 is increased, the two expand equally, and therefore no compressive stress or tensile stress is generated in the observation region 17d of the sample 17b.
When the thermal expansion coefficient _α1 of the sample 17b to be observed is larger than the thermal expansion coefficient _α2 of the auxiliary plate 17a, the sample 17b expands more than the auxiliary plate 17a as shown in Fig. 2(b), and thus, when the temperature of the sample assembly 17 is increased, a compressive stress is generated in the observation region 17d of the sample 17b. When the thermal expansion coefficient _α1 of the sample 17b to be observed is extremely larger than the thermal expansion coefficient α2 of the auxiliary plate 17a, similarly, when the temperature of the sample assembly 17 is increased, a compressive stress is generated in the observation region 17d of the sample 17b. Due to the deformation of the observation region 17d in the center of the sample 17b, _a difference in stress occurs between the upper and lower surfaces of the observation region 17d.
When the thermal expansion coefficient _α1 of the sample 17b to be observed is smaller than the thermal expansion coefficient _α2 of the auxiliary plate 17a, the amount of expansion of the sample 17b is smaller than that of the auxiliary plate 17a, as shown in FIG. 2(c), so that tensile stress is generated in the observation region 17d of the sample 17b when the temperature of the sample assembly 17 is increased.

In summary, when compressive stress is to be created in the observation area 17d of the sample 17b, it can be achieved by bonding the sample 17b to an auxiliary plate 17a having a larger thermal expansion coefficient than the sample 17b and then cooling it, or by bonding the sample 17b to an auxiliary plate 17a having a smaller thermal expansion coefficient than the sample 17b and then heating it. Conversely, when tensile stress is to be created in the observation area 17d of the sample 17b, it can be achieved by bonding the sample 17b to an auxiliary plate 17a having a larger thermal expansion coefficient than the sample 17b and then heating it, or by bonding the sample 17b to an auxiliary plate 17a having a smaller thermal expansion coefficient than the sample 17b and then cooling it.

In addition, when the sample 17b and the auxiliary plate 17a are bonded at a high temperature, it is necessary to calculate the stress generated at the temperature at which the transmission diffusion path and the like are observed, based on the temperature at which the sample 17b and the auxiliary plate 17a are bonded. For example, by cooling the sample bonded body 17 bonded at a high temperature to room temperature, stress can be generated in the observation region 17d of the sample 17b.
For example, as shown in Fig. 2(c) above, if the thermal expansion coefficient _α1 of sample 17b is smaller than the thermal expansion coefficient _α2 of auxiliary plate 17a, the auxiliary plate 17a will shrink significantly when they are joined at a high temperature and cooled to room temperature. On the other hand, sample 17b, which has a lower thermal expansion coefficient than auxiliary plate 17a, does not shrink much, so that sample 17b acts against the shrinkage of auxiliary plate 17a, and as a result, a compressive stress is created in observation region 17d of sample 17b by auxiliary plate 17a at room temperature. In order to create a larger compressive stress, sample 17b and auxiliary plate 17a should be joined by cooling them to a low temperature.
2B, when the thermal expansion coefficient _α1 of the sample 17b is larger than the thermal expansion coefficient _α2 of the auxiliary plate 17a, when the sample 17b is joined at a high temperature and cooled to room temperature, the auxiliary plate 17a does not shrink much, whereas the sample 17b shrinks significantly. As a result, tensile stress is generated in the observation area 17d of the sample 17b at room temperature.
Thus, the generation of stress is affected by the history of bonding between the sample 17b and the auxiliary plate 17a, but in any case, it is possible to create a desired stress by calculation and temperature.

(Example of stress generation)
As shown in FIGS. 1(a) and 1(b), a sample assembly 17 was prepared by joining a circular membrane-shaped sample 17b to a ring-shaped auxiliary plate 17a having an opening 17c at its center. The stress generated in the sample 17b was measured.

3 is a diagram for explaining a method of calculating the stress caused by the difference in the thermal expansion coefficient between the bonded sample 17b and auxiliary plate 17a. When _α1 is the linear expansion coefficient of the sample 17b to be measured, _α2 is the linear expansion coefficient of the auxiliary plate 17a, Δt is the temperature difference, E is Young's modulus, ν is Poisson's ratio, _r0 is the outer diameter of the sample 17b, _r1 is the inner diameter of the auxiliary plate 17a, and _σ1 is the stress at the position of radius _r1 of the sample 17b, the stress caused in the sample 17b can be calculated using the following formulas eq(1), eq(2), and eq(3).

That is, in the sample assembly 17 shown in Fig. 3(a), when the sample 17b and the auxiliary plate 17a are not integrated as shown in Fig. 3(b), the displacement _Δr1 of the sample 17b when a temperature change of Δt occurs at a point of radius _r1 is expressed as _r1α1Δt . Similarly, the displacement of the auxiliary _{plate 17a is r1α2Δt ,} and a gap of _r1Δt ( _α1 - _α2 ) is generated between the sample 17b and the auxiliary plate 17a as shown in equation (1).

In reality, since the sample 17b and the auxiliary plate 17a are joined together as shown in Fig. 3(c), this gap in displacement must be offset by elastic deformation. If the auxiliary plate 17a has sufficient rigidity with respect to the sample 17b, it can be considered that elastic deformation occurs only in the sample 17b.
If the stress acting to contract the sample 17b is σ ₁ , the displacement Δr ₁ due to elastic deformation can be expressed as −r ₁ σ ₁ /E(1−ν).
As a result, from equations Eq(1) and Eq(2), the stress σ ₁ can be obtained as −EΔt(α ₁ −α ₂ )/(1−ν), as shown in equation (3).

In addition, inside a plate that receives a constant pressure from the outer periphery, a two-dimensional stress field is formed in which a uniform normal stress that is independent of location and direction acts, so when r< _r1 , a uniform stress _σ1 = _σθ = _σr ( _σθ is the circumferential stress, and _σr is the radial stress) acts.
Here, since the formula eq(3) does not depend on the radius, the generated stress is determined regardless of the inner radius _r1 of the auxiliary plate 17a. In other words, the applied stress is determined only by the difference in linear expansion coefficient, temperature, Poisson's ratio, and elastic coefficient, and does not depend on the sample dimensions. In reality, the stress due to gas pressure is superimposed on this.
This makes it possible to obtain the stress generated in the sample 17b.

(Observation equipment)
Next, an observation device for observing the permeation diffusion path of the observation target gas in the sample 17b using such a sample assembly 17 will be described. In this embodiment, the observation target gas is hydrogen, but the present invention is not limited thereto. The observation target gas may be deuterium, helium, oxygen, nitrogen, water, or a molecule or ion derived from any of the gases used for various purposes during sample preparation or sample use, or molecules or ions derived from a plurality of gases among them. In this embodiment, deuterium may be used so that it can be easily distinguished from hydrogen gas remaining as a background.

In this embodiment, a hydrogen permeation diffusion path observation device, which is one type of observation target gas observation device, will be described. In the following description, the observation target ions will be hydrogen ions, the observation target gas supply unit will be a hydrogen gas supply unit, and the observation target ion detection unit will be a hydrogen ion detection unit.
FIG. 4 is a schematic diagram showing the configuration of the hydrogen permeation diffusion path observation device 10 according to the embodiment, and FIG. 5 is a partially enlarged diagram showing the hydrogen ion detection unit 20 in the analysis chamber 11 and the mounting structure of the diaphragm-type vacuum vessel 12, etc.

The hydrogen permeation diffusion path observation device 10 is equipped with a scanning electron microscope 15. The scanning electron microscope 15 is equipped with an analysis chamber 11 that can accommodate a sample assembly 17 and create a high degree of vacuum, an electron source 16 that irradiates an electron beam onto the sample 17b of the sample assembly 17 in the analysis chamber 11, a secondary electron detector 18 that detects secondary electrons generated by the electron beam irradiated onto the sample 17b, a sample position adjustment unit 34 for adjusting the position of the sample assembly 17, and a first vacuum exhaust unit 37 for evacuating the analysis chamber 11.

The hydrogen permeation diffusion path observation device 10 includes a diaphragm-type vacuum vessel 12 in which a sample assembly 17 arranged in an analysis chamber 11 can be detachably attached, a temperature control unit 30 that adjusts the temperature of the sample assembly 17 attached to the diaphragm-type vacuum vessel 12, a hydrogen gas supply unit 19 that supplies hydrogen from a hydrogen pipe 14 into the diaphragm-type vacuum vessel 12, an electron source 16 that irradiates an electron beam onto the sample assembly 17, a hydrogen ion detection unit 20 that detects hydrogen ions generated by the electron beam irradiated from the electron source 16, and a control unit 50 that controls each unit.

The analysis chamber 11 of the scanning electron microscope 15 is equipped with a diaphragm-type vacuum vessel 12 in which the sample assembly 17 can be mounted, a sample stage 31 on which the diaphragm-type vacuum vessel 12 is mounted, a sample temperature measurement unit 33 that measures the temperature of the sample assembly 17, and a sample position adjustment unit 34 that adjusts the position of the sample assembly 17.

The first vacuum exhaust unit 37 is configured to include a vacuum pump such as a turbo molecular pump (not shown), a gate valve, a vacuum gauge, etc., and can create an ultra-high vacuum state as an observation atmosphere inside the analysis chamber 11. This allows the analysis chamber 11 to be evacuated to a vacuum level at which an SEM image can be obtained, for example, 1.0×10 ⁻⁷ Pa or less.

The analysis chamber 11 may be equipped with a mass analyzer 35 or the like for analyzing the residual elements in the analysis chamber 11. The mass analyzer 35 is, for example, a quadrupole mass spectrometer. The analysis chamber 11 may further be equipped with an Auger electron spectrometer 36. The Auger electron spectrometer 36 can measure the amount of carbon and the like present on the surface of the sample 17b. In addition, the background of hydrogen, carbon, and the like present on the surface of the sample 17b may be removed by a sputtering source or electron beam irradiation provided in the analysis chamber 11 before acquiring an ESD image, which will be described later.

Figure 6 is a cross-sectional view showing a schematic diagram of the diaphragm-type vacuum vessel 12 of this embodiment. The diaphragm-type vacuum vessel 12 of the hydrogen permeation diffusion path observation device 10 includes a vessel body 12a formed smaller than the analysis chamber 11 and capable of being entirely accommodated within the analysis chamber 11, a hollow portion 12c provided within the vessel body 12a and supplied with hydrogen gas, a sample mounting portion 12b provided at the top of the vessel body 12a and capable of mounting a sample assembly 17, an opening window 12e of the hollow portion 12c provided in the sample mounting portion 12b, and a second vacuum exhaust portion 38 for exhausting the hollow portion 12c.

The container body 12a is required to emit little hydrogen gas, so it is made of ultra-high vacuum materials such as stainless steel, copper, and glass, and when heated, is made of a material that can be baked at, for example, 120°C. The sample mounting section 12b can be made of copper to improve thermal conductivity.

The sample mounting section 12b is a mounting site for the sample assembly 17 including the sample 17b to be observed, which is provided on the upper part of the container body 12a, has an opening window 12e in the hollow section 12c, and is formed in a shape corresponding to the rear surface of the sample assembly 17. In this embodiment, a window frame area is provided surrounding the periphery of the opening window 12e to which the sample assembly 17 is abutted, and a seal portion or the like is provided in the window frame area as appropriate. The sample assembly 17 is mounted on the sample mounting section 12b with the opening window 12e blocked.

The sample assembly 17 mounted on the sample mounting section 12b may have any shape that can close the opening window 12e, and may be, for example, a disk shape with a diameter of 8 mm and a thickness of 1 mm. The sample assembly 17 may be held at its outer periphery by being pressed against the sample mounting section 12b from the upper side of the sample mounting section 12b by a sample fixing plate (not shown). The thickness of the measurement portion of the sample 17b of the sample assembly 17 arranged as a diaphragm may be approximately the same as the size of the crystal grains of the sample, and may be, for example, about 100 to 300 μm.

As shown in Fig. 4, the hydrogen gas supply unit 19 is connected to the diaphragm-type vacuum vessel 12 via the hydrogen pipe 14 and the sample stage 31. The hydrogen gas supply unit 19 is configured to include a hydrogen gas cylinder (not shown), a pressure regulator, a stop valve, a pressure gauge, etc. After the hydrogen pipe 14, the sample stage 31, and the diaphragm-type vacuum vessel 12 are evacuated to a predetermined degree of vacuum, the stop valve on the second vacuum exhaust unit 38 side is closed to maintain a constant degree of vacuum. The predetermined degree of vacuum is, for example, 8.0 x ^10-4 Pa or less.

As shown in FIG. 6, the temperature control unit 30 may be any unit that controls the temperature of the sample assembly 17 by at least one of heating and cooling the sample assembly 17 mounted in the diaphragm-type vacuum vessel 12, but in this embodiment, it includes a sample heating unit 32, a sample cooling unit 29, a sample temperature measuring unit 33 that measures the temperature of the sample assembly 17, and a temperature control unit 28 that controls the sample heating unit 32 and the sample cooling unit 29.

The sample heating section 32 can be composed of a heater, halogen lamp, etc., that heats the sample assembly 17 in the diaphragm-type vacuum container 12 or the sample stage section 31. In this embodiment, the heating for applying stress is performed by a heater arranged below the sample assembly 17. When a heater is used, the temperature can be easily controlled by PID control of the output, etc.

The sample cooling unit 29 may also be a general means, and is provided in the diaphragm-type vacuum vessel 12 or the sample stage 31, etc., to cool the sample assembly 17. In this embodiment, the cooling for applying stress comprises a cooling plate 29a attached to the diaphragm-type vacuum vessel 12, a cold finger 29c connected to the cooling plate 29a for cooling the sample assembly 17 using thermal conduction, and a cooling medium bath 29b of liquid nitrogen, cooled helium gas, or the like. The cold finger 29c has a movable structure that can be removed from the cooling plate 29a, thereby preventing heat from leaking out during heating.

The sample temperature measuring unit 33 can measure the temperature by measuring the electromotive force generated in the thermocouple due to the temperature of the sample assembly 17 with a voltmeter connected to the external terminal of the conductor lead-out port 11a. The temperature control unit 28 controls one or both of the sample cooling unit 29 and the sample heating unit 32 so that the temperature of the sample assembly 17 becomes the desired observation temperature in order to generate the desired stress in the observation area 17d of the sample 17b. By controlling using, for example, PID control, the stress generated in the observation area 17d of the sample 17b of the sample assembly 17 can be kept at a constant value.

As shown in FIG. 5, the hydrogen ion detection unit 20 is composed of a collection mechanism 21 that collects hydrogen ions generated from the surface of the sample 17b of the sample assembly 17 mounted in the diaphragm-type vacuum container 12, an ion energy decomposition unit 22 that removes ions other than hydrogen ions, and an ion detector 23 that detects hydrogen ions that have passed through the ion energy decomposition unit 22.

Hydrogen gas is supplied from the hydrogen gas supply unit 19 to the diaphragm-type vacuum vessel 12 and is present inside the diaphragm-type vacuum vessel 12. The hydrogen gas is in contact with the rear side of the sample assembly 17, and is introduced into the inside of the sample 17b from the rear side of the sample assembly 17. This hydrogen diffuses inside the sample 17b, reaches the front surface of the sample 17b, and is released from the surface of the sample 17b. In other words, hydrogen and deuterium penetrate from the rear side of the observation region 17d of the sample 17b to the front surface. By irradiating the hydrogen that has reached the surface of the sample 17b with the electron beam 16a, hydrogen ions are desorbed from the sample 17b by electron stimulated desorption (ESD), and these hydrogen ions 41 are collected by the collection mechanism 21 and detected by the hydrogen ion detection unit 20.

The hydrogen ion detector 20 detects hydrogen ions generated on the surface of the sample 17b by the ESD method. The two-dimensional image of hydrogen ions detected by scanning the electron beam 16a is also called an ESD image or ESD map.

A collection mechanism 21 is disposed near the surface side of the sample assembly 17 to efficiently collect desorbed ions. The illustrated collection mechanism 21 is, for example, a lens with a grid structure made of a metal wire mesh. Ions of the target gas collected by the collection mechanism 21, for example hydrogen ions, enter the hydrogen ion detection section 20. In the ion energy decomposition section 22, for example hydrogen ions are selected and made to enter the ion detector 23.

The ion energy decomposition section 22 is made of a metal electrode having a lid shape so that the ion detector 23 does not directly face the sample assembly 17. The ion energy decomposition section 22 can use an electrode having a shape including a cylindrical shape or a cone shape. The ion energy decomposition section 22 applies an appropriate positive voltage to the cylindrical electrode, and can guide only the ions of the target gas, for example, hydrogen ions, to the ion detector 23 by the electric field, and can remove the light and electrons generated when the sample assembly 17 is irradiated with the electron beam 16a. The ion detector 23 can be, for example, a Ceratron or a secondary electron multiplier.

Figure 7 is a block diagram of the control unit 50, and Figure 8 is a block diagram showing the configuration of the electron stimulated desorption overall control unit 52. As shown in Figure 7, the control unit 50 is configured to include an electron microscope overall control unit 51 that controls the scanning electron microscope 15, and an electron stimulated desorption overall control unit 52 that controls the acquisition of ESD images.

The control unit 50 includes, in addition to the electron microscope overall control unit 51, a secondary electron detection unit 53 to obtain a scanning electron microscope image (SEM image) of the sample joint 17, an electron optical system control unit 54, an image calculation unit 55 for SEM, a high-voltage stabilized power supply 56, an input device 57, a display 58, a storage device 59, etc. The electron microscope overall control unit 51 is configured to control each of the secondary electron detection unit 53, the electron optical system control unit 54, the image calculation unit 55 for SEM, the high-voltage stabilized power supply 56, and the storage device 59. The output of the secondary electron detector 18 disposed in the analysis chamber 11 is input to the secondary electron detection unit 53.

As shown in FIG. 8, the electronically stimulated desorption overall control unit 52 is composed of a two-dimensional multichannel scaler 60, a pulse counting unit 61, a synchronization control unit 62, a unit 63 for rearranging the measurement signals onto a two-dimensional plane, a microprocessor 72, etc.

The output of the ion detector 20 disposed in the analysis chamber 11 is input to the pulse counter 61 via the electron stimulated desorption ion detector 67 as output 67a. A scanning signal is input from the electron optical system controller 54 to the electron stimulated desorption overall controller 52, which is controlled in synchronization with the SEM image. A display 65 and a storage device 66 are further connected to the electron stimulated desorption overall controller 52.

The microprocessor 72 may be a microcomputer such as a microcontroller, a personal computer, or an FPGA (Field-Programmable Gate Array), which is a gate array that can be programmed on the field.

In this electron stimulated desorption overall control unit 52, the scanning signal input from the electron optical system control unit 54 to the synchronization control unit 62 is output as a vertical scanning signal 62a via the synchronization control unit 62 to the first deflection coil 16b of the electron source 16.

The horizontal scanning signal 62b from the synchronization control unit 62 is output to the second deflection coil 16c of the electron source 16. Information 62c relating to the scanning position is output from the synchronization control unit 62 to the microprocessor 72.

The hydrogen ion count signal 61a output from the pulse counter 61 is output to the microprocessor 72 as a hydrogen ion count signal for each scanning position. The hydrogen ion counts for each sample position counted by the pulse counter 61 can be integrated by acquiring an ESD image for a specified imaging time to obtain the distribution of hydrogen ions that have passed through the sample 17b.

The ESD image generated by the microprocessor 72 is output to the display 65 via the input/output interface (I/O) 72a, and is also output to the storage device 66 via the input/output interface (I/O) 72b.

Figure 9 is a schematic diagram showing the relationship between the scanning of the electron source 16 and the two-dimensional measurement of the ESD image. As shown in Figure 9, the electron beam 16a generated from the electron source 16 passes through the first deflection coil 16b and the second deflection coil 16c, and is scanned vertically and horizontally to be irradiated two-dimensionally onto the sample 17b.

The clock signal of the vertical scanning signal, which is a digital signal generated by the synchronization control unit 62 shown in FIG. 9, is converted to a sawtooth wave by a digital-to-analog converter (DAC) 62d and applied to the first deflection coil 16b of the electron source 16. Similarly, the clock signal of the horizontal scanning signal, which is a digital signal, is converted to a sawtooth wave by a digital-to-analog converter (DAC) 62e and applied to the second deflection coil 16c of the electron source 16.

A one-pulse shooting timing signal (called the Shoot timing, ST signal) initiates control so that a total of 2048 pulses of the vertical scanning signal (Vertical clock) are generated.

During the pulse width of one pulse of the vertical scanning signal, a total of 2048 pulses of horizontal pixel signals (Horizontal clock) are output. This generates a two-dimensional scan of approximately 4.19 million pixels, or 2048 rows x 2048 columns (=4194304). In other words, the signal counted by the pulse counting unit 61 can be obtained as the number of hydrogen ions counted from the ion detector 23 at each scanning position by synchronizing multiple counters consisting of the ST signal, a clock signal for vertical scanning, and a clock signal for horizontal scanning.

10 is a flow diagram of measuring a two-dimensional ESD image by scanning. As shown in this figure, acquisition of a two-dimensional ESD image can be performed in the following steps.
Step 1: Ions desorbed from the surface of the sample 17b are detected by the ion detector 23.
Step 2: The ions detected by the ion detector 23 are quantitatively measured by the pulse counter 61 .
Step 3: Ions at each two-dimensional measurement point on the sample 17b are counted by the synchronization control unit 62 which generates a clock signal for vertical scanning and a clock signal for horizontal scanning shown in FIG.

Step 4: The ion counts at each two-dimensional measurement point of the sample 17b measured in step 3 are stored in the memory of the storage device 66.
Step 5: The ion signals stored in the memory of the storage device 66 are rearranged into a two-dimensional image based on the clock signal for vertical scanning and the clock signal for horizontal scanning.
Step 6: The ESD image acquired in step 5 is displayed on the display 65 and stored in the storage device 66 as image and numerical data.
This allows an ESD image of the same area as the SEM image to be acquired.

The acquisition of the ESD image in steps 1 to 6 above can be performed using software created in a program creation environment specialized for measuring instrument control. One such software that can be used is National Instruments' LabVIEW (registered trademark) (http://www.ni.com/labview/ja/). The ESD image in steps 1 to 6 above can be acquired using a two-dimensional multichannel scaler 60 that is executed by a program created in LabVIEW in the microprocessor 72.

(Method of observing hydrogen ions)
Next, a method for observing hydrogen ions passing through the sample 17b using the above-described sample bonded assembly 17 will be described.
First, a film-like sample 17b to be measured is bonded to a ring-shaped auxiliary plate 17a to prepare a sample bonded assembly 17 as shown in Fig. 1. The material of the auxiliary plate 17a, the bonding temperature between the sample 17b and the auxiliary plate 17a, etc. are selected based on the desired measurement temperature during observation and the desired stress to be generated in the sample 17b during observation.

The prepared sample assembly 17 is attached to the sample mounting portion 12b of the diaphragm-type vacuum vessel 12 as shown in FIG. 6, and is placed together with the diaphragm-type vacuum vessel 12 in the analysis chamber 11 of the scanning electron microscope 15. The sample assembly 17 is placed so as to cover the opening window 12e communicating with the inside of the diaphragm-type vacuum vessel 12, and is attached in a sealed state to the upper surface of the sample mounting portion 12b with the lower surface of the auxiliary plate 17a as the sealing surface. The sample assembly 17 may be turned upside down so that the sample 17b serves as the sealing surface. The diaphragm-type vacuum vessel 12 with the sample assembly 17 fixed thereto is placed in the analysis chamber 11 of the scanning electron microscope 15, and the hollow portion 12c of the diaphragm-type vacuum vessel 12 and the analysis chamber 11 are partitioned by the sample 17b, which is a part of the sample assembly 17. This allows the hollow portion 12c to communicate with the opening 17c of the auxiliary plate 17a, and the observation area 17d acts as a partition separating the analysis chamber 11 from the hollow portion 12c.

The analysis chamber 11 is placed in an ultra-high vacuum state, and hydrogen is supplied from the hydrogen gas supply unit 19 to the hollow portion 12c of the diaphragm-type vacuum vessel 12. Next, the temperature of the sample assembly 17 is heated or cooled by the temperature control unit 30 to the desired temperature, thereby generating the desired stress, such as tensile stress or compressive stress, in the observation area 17d of the sample 17b. Because a material with an appropriate thermal expansion coefficient is selected in advance for the auxiliary plate 17a, and the sample 17b and the auxiliary plate 17a are joined at an appropriate temperature, it is possible to precisely generate stress by adjusting the temperature of the sample assembly 17 to the planned observation temperature.

Then, while the hydrogen gas in the hollow portion 12c of the diaphragm-type vacuum vessel 12 is brought into contact with the rear surface of the observation region 17d of the sample 17b, the electron beam 16a is irradiated onto the surface of the observation region 17d, whereby the ions to be observed are generated and detected, and an SEM image and an ESD image are obtained.

According to the sample joint 17 of this embodiment, the sample 17b having the observation area 17d and the annular auxiliary plate 17a having a thermal expansion coefficient different from that of the sample 17b and an opening at a position corresponding to the observation area 17d are joined in a laminated state. Therefore, when the observation temperature is set to a temperature different from the temperature at which the sample 17b and the auxiliary plate 17a are joined, the sample 17b and the auxiliary plate 17a thermally expand or contract, respectively, and stress can be generated in the observation area 17d of the sample 17b placed at the opening of the auxiliary plate 17a due to the temperature difference and the thermal expansion coefficient difference between the time of joining and the time of observation.

This allows the desired stress to be generated by selecting the combination of materials for the sample 17b and the auxiliary plate 17a, the shape, size, thickness, etc., and the temperature during bonding and observation temperature, etc. For example, by mechanically creating a stress concentration point, it is possible to increase the strength of the stress that can be applied even in a narrow temperature range. Therefore, when observing hydrogen ions generated by irradiating the electron beam 16a onto the surface of the sample with hydrogen gas in contact with the back surface of the sample, it is possible to generate the desired stress in the observation area 17d of the sample 17b without contact, without pushing up the observation area 17d of the sample 17b with an indenter or the like.

According to the sample assembly 17 of this embodiment, the sample 17b has an observation area 17d on the inside separated from the periphery, and the auxiliary plate 17a is joined to the sample 17b around the entire circumference of the annular opening 17c, so that when stress is generated in the observation area 17d of the sample, a load can be applied evenly from the entire circumference. In the sample assembly 17, the sample 17b and the auxiliary plate 17a are joined at a temperature different from the observation temperature, so that stress can be reliably generated by setting the temperature to the planned observation temperature during observation.

In the sample joint 17, the sample 17b and the auxiliary plate 17a are directly joined without a stress relaxation layer. Therefore, when a difference in thermal expansion occurs between the sample 17b and the auxiliary plate 17a, the difference is not relaxed by other materials, but can be directly converted into stress generated in the observation area 17d, and the desired stress can be easily generated.

According to the hydrogen permeation diffusion path observation device 10 and the hydrogen ion observation method of this embodiment, the sample assembly 17 is mounted in the diaphragm-type vacuum vessel 12 so that the observation region 17d of the sample 17b separates the hollow portion 12c from the analysis chamber 11, hydrogen gas in the hollow portion 12c is brought into contact with the back surface of the observation region 17d of the sample 17b, and the sample surface is irradiated with the electron beam 16a to generate hydrogen ions. The hydrogen ion detection unit 20 can detect the emergence of hydrogen ions and obtain the count number of the emerged hydrogen ions. In other words, a two-dimensional ESD image can be obtained together with an SEM image, and the emergence distribution of hydrogen ions in the observation region 17d of the sample 17b can be measured. At that time, the temperature control unit 30 can adjust the sample assembly 17 to a desired temperature to generate a desired stress in the observation region 17d of the sample 17b. Therefore, by using the above-mentioned sample assembly 17, it is possible to detect hydrogen ions in a state in which a desired stress is generated in the observation region 17d of the sample 17b without contact.
Therefore, the hydrogen permeation diffusion path observation device 10 and the hydrogen ion observation method suitable for observing hydrogen gas using the sample bonded body 17 can be realized.

According to the observation device 10 and observation method of this embodiment, the temperature of the sample assembly 17 can be adjusted to a desired temperature by the temperature adjustment unit 30, and the desired stress can be easily generated in the observation area 17d of the sample 17b. Furthermore, by keeping the sample assembly 17 at a desired temperature, the observation area 17d of the sample 17b can be easily maintained in a state in which the desired stress is generated.

The above embodiment can be modified as appropriate within the scope of the present invention.
For example, in the above embodiment, hydrogen is used as the gas to be observed, but the gas to be observed is not limited to hydrogen and other gases can also be used. The present invention can be applied to any gas that produces ions to be observed when brought into contact with the back surface of sample 17b and irradiated with an electron beam on the front surface.

10: Hydrogen permeation diffusion path observation device 11: Analysis chamber 12: Diaphragm-type vacuum vessel 12a: Vessel body 12b: Sample mounting section 12c: Hollow section 15: Scanning electron microscope 16: Electron source 16a: Electron beam 16b: First deflection coil 16c: Second deflection coil 17: Sample assembly 17a: Auxiliary plate 17b: Sample 17c: Opening 17d: Observation area 12e: Opening window 18: Secondary electron detector 19: Hydrogen gas supply section (observation target gas supply section) 20: Hydrogen ion detection section (observation target ion detection section) 21: Collection mechanism 22: Ion energy resolution section 23: Ion detector 28: Temperature control section 29: Sample cooling section 29a: Cooling plate 29b: Cooling medium bath 29c: Cold finger 30: Temperature adjustment section 31: Sample stage section 32: Sample heating section 33: Sample temperature measuring section 34: Sample position adjustment section 35: Mass analyzer 36: Auger electron spectrometer 37: First vacuum exhaust section 38: Second vacuum exhaust section 50: Control section 51: Electron microscope overall control section 52: Electron stimulated desorption overall control section 53: Secondary electron detection section 54: Electron optical system control section 55: SEM image calculation section 56: High voltage stabilized power supply 57: Input device 58, 65: Display 59, 66: Storage device 60: Two-dimensional multi-channel scaler 61: Pulse counter section 61a: Hydrogen ion count number signal 62: Synchronization control section 62a: Vertical scanning signal 62b: Horizontal scanning signal 62c: Information regarding scanning position 62d, 62e: Digital-to-analog converter 63: Measurement signal rearrangement section onto two-dimensional plane 67: Electron stimulated desorption ion detection section 72: Microprocessor 72a, 72b: Input/output interface

Claims (7)

1. A sample assembly comprising: a sample for ionizing an observation target gas that has penetrated from the back side to the front side and observing the ions in an observation device; and an auxiliary plate to be placed on the back side of the sample, wherein the sample has an observation area set at the center of its front side, the auxiliary plate has a thermal expansion coefficient different from that of the sample, has an opening at a position corresponding to the observation area of the sample , has approximately the same outer shape as the sample, and is directly bonded to the sample in a laminated state around the entire periphery of the opening without a stress relaxation layer, the sample and the auxiliary plate are bonded at a bonding temperature different from the temperature during observation in the observation device, and a stress is applied to the observation area of the sample to observe the ions . The sample assembly according to claim 1, wherein the thickness of the observation area in the sample is approximately the same as the size of the crystal grains in the sample. The sample conjugate according to claim 1 or 2, wherein the thickness of the observation region is 100 to 300 μm. A sample assembly according to any one of claims 1 to 3, wherein the thickness of the auxiliary plate is greater than that of the sample. An observation device for observing the ions of the observation target gas by mounting the sample conjugate according to any one of claims 1 to 4, comprising: a scanning electron microscope for detecting secondary electrons generated by irradiating the observation region of the sample with an electron beam in an analysis chamber; a vacuum vessel having a hollow portion into which the observation target gas is introduced and in which the sample conjugate is mounted so as to separate the hollow portion from the analysis chamber by the sample; a temperature adjustment unit for adjusting the temperature of the sample conjugate mounted in the vacuum vessel; and an observation target ion detection unit capable of detecting observation target ions generated by bringing the observation target gas introduced into the hollow portion into contact with the rear surface of the sample and irradiating the observation region on the surface of the sample with an electron beam. The observation device for an observation target gas as described in claim 5, wherein the temperature adjustment unit includes a heating and cooling unit that heats and cools the sample assembly mounted in the vacuum vessel, and a temperature control unit that controls the heating and cooling unit to adjust the temperature of the sample assembly. An observation method for measuring the ions of the observation target gas using the sample assembly according to any one of claims 1 to 4, comprising the steps of: mounting the sample assembly in a vacuum container so as to separate a hollow space from an analysis chamber by the sample, and arranging the sample assembly in the analysis chamber of a scanning electron microscope; setting the temperature of the sample assembly to the observation temperature; and detecting ions generated by bringing the observation target gas introduced into the hollow space into contact with the rear surface of the sample and irradiating the observation region on the surface of the sample with an electron beam.

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