Microscope system

Abstract

The purpose of the present invention is to provide a microscope system capable of isolating electron wave information derived from a plurality of layers, from electron waves that have passed through the layers including a sample and that have been acquired by a microscope, and thereby improving the image quality of the sample that is observed. The microscope system according to the present invention comprises: a microscope that causes incoming electron beams to be deflected on a first layer, a second layer, and a third layer to obtain multiple sets of electron wave information; and a control device that changes the positions of focal points in the plurality of sets of electron wave information obtained by the microscope to the third layer, and calculates the amplitudes and phases of electron waves derived from the first layer, the second layer, and the third layer, on the basis of amplitudes and phases included the electron wave information after the changing of the focal points.

Description

Technical Field

[0001] The present invention relates to a microscope system.

Background Art

[0002] In order to achieve carbon neutrality, it is essential to elucidate the reaction mechanism of catalysts in high-efficiency hydrogen production, artificial photosynthesis, and fuel cells. In recent years, there has been an increasing demand for in-situ observation of the morphological and physical property changes of catalysts during actual operation, that is, in a gas environment or a liquid environment, using an electron microscope. When performing in-situ observation, a diaphragm-type environmental control holder has attracted attention because it is a powerful method for introducing atmospheric gas or liquid into the holder. For example, Patent Document 1 discloses a method of enclosing a liquid and a gas in a diaphragm-type holder having a sealed region and observing a sample.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a diaphragm-type holder, since the electron beam penetrates not only the sample but also the diaphragms above and below the sample, the signal from the diaphragm may be superimposed on the signal from the sample, and the image quality of the sample may deteriorate. In particular, the reaction field (electromagnetic field) that affects the characteristics of chemical reactions such as catalysts and electrodes is a very small signal, and ultra-high-precision measurement is required for its analysis. Therefore, the deterioration of the image quality of the sample can be fatal.

[0005] An object of the present invention is to provide a microscope system capable of separating the electron wave transmitted through a plurality of layers including a sample acquired by a microscope into electron wave information derived from each layer and enhancing the image quality of the sample to be observed.

Means for Solving the Problems

[0006] To solve the above problems, the microscope system of the present invention includes a microscope that deflects an incident electron beam with respect to a first layer, a second layer, and a third layer to acquire a plurality of electron wave information, and changes a focal position of the plurality of electron wave information acquired by the microscope to the third layer, and based on the amplitude and phase included in the electron wave information after the focal position change, calculates the amplitude and phase of the electron waves derived from the first layer, the second layer, and the third layer, respectively, and a control device.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a microscope system capable of separating, for an electron wave transmitted through a plurality of layers including a sample, acquired by a microscope, into electron wave information derived from each layer, and enhancing the image quality of the sample to be observed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In all the drawings, the same members are basically denoted by the same reference numerals, and the repeated description thereof will be omitted.

Examples

[0010] The microscope system according to Example 1 will be described. FIG. 1 is a schematic diagram of the microscope system. As shown in FIG. 1, the microscope system includes a transmission electron microscope 1 and a control device 2 (analysis PC).

[0011] First, the configuration of the transmission electron microscope 1 will be described. The transmission electron microscope 1 includes an electron source 4, a condenser lens 5, a deflector 6, an objective lens 7, an electron biprism 8, an imaging lens system 9, a fluorescent plate 10, a camera 11, a goniometer 12, a control PC 15, and a display device 16.

[0012] The electron source 4 includes a cathode that emits an electron beam 3 and an acceleration tube that accelerates the electron beam 3. The condenser lens 5 converges the electron beam 3 emitted and accelerated by the electron source 4. The deflector 6 deflects the incident angle of the electron beam 3 converged by the condenser lens 5. The objective lens 7 is a lens that adjusts the size of the electron beam 3 irradiated on the sample 40, and has an upper electrode plate disposed upstream of the electron beam 3 and a lower electrode plate disposed downstream of the electron beam 3. The electron biprism 8 overlaps the electron wave that has passed through the sample 40 to be observed and the reference electron wave that serves as a phase reference with each other to form an electron interference fringe (hologram). The imaging lens system 9 is a plurality of lenses for magnifying and imaging the hologram. The fluorescent plate 10 is a plate that emits fluorescence by the electron beam 3 imaged by the imaging lens system 9. The camera 11 (imaging unit) acquires the hologram image obtained by the imaging lens system 9 when the fluorescent plate 10 is opened.

[0013] The goniometer 12 adjusts the position of the sample holder 13 to be mounted. Further, when the sample holder 13 is mounted on the goniometer 12, the diaphragm holder 14 provided at the tip of the sample holder 13 comes to be positioned between the upper electrode piece and the lower electrode piece of the objective lens 7. Here, the diaphragm holder 14 supports the sample 40 to be observed and is separated from the sample 40 by a first membrane 41 on the upper side and a second membrane 42 on the lower side of the sample 40 so that a gas or liquid at atmospheric pressure can be introduced. Therefore, the sample holder 13 and the goniometer 12 can be regarded as a holding part that holds the first membrane 41, the sample 40, and the second membrane 42. In the following description, the first membrane 41 may be referred to as the first layer, the sample 40 as the second layer, and the second membrane 42 as the third layer.

[0014] The control PC 15 controls the electron source 4, the condenser lens 5, the deflector 6, the objective lens 7, the electron biprism 8, the imaging lens system 9, the camera 11, and the goniometer 12, and stores the hologram image acquired by the camera 11 in a storage part (not shown). The display device 16 outputs the control content of the control PC 15, the hologram image acquired by the camera 11, etc., and is, for example, a display.

[0015] In the transmission electron microscope 1 having the above-described configuration, the electron beam 3 emitted from the electron source 4 passes through the condenser lens 5 and the upper magnetic pole piece of the objective lens 7 and is irradiated onto the diaphragm holder 14. The electron beam 3 that has passed through the diaphragm holder 14 passes through the lower magnetic pole piece of the objective lens 7 and the imaging lens system 9 composed of a plurality of lenses. When the fluorescent plate 10 is open, the electron wave information acquired by the camera 11 is output to the display device 16. Further, in the above-described transmission electron microscope 1, since the electron biprism 8 is provided between the diaphragm holder 14 and the imaging lens system 9, electron holography observation capable of acquiring the phase information of the electron wave can be performed. The number of electron biprisms 8 is not particularly limited and may be two. Furthermore, as long as the phase information of the electron wave can be acquired, methods other than electron holography or other charged particle devices, for example, a scanning transmission electron microscope or a scanning electron microscope, etc. may be used.

[0016] Next, the configuration of the control device 2 (analysis PC) will be described. The control device 2 changes the focal position of a plurality of electron wave information (for example, a hologram image) stored in the storage unit of the control PC 15 to the second film 42, and based on the amplitude and phase included in the electron wave information after the focal position change, calculates the amplitude and phase of the electron waves derived from the first film 41, the sample 40, and the second film 42. The data exchange between the control PC 15 of the transmission electron microscope 1 and the control device 2 may be performed via a dedicated communication line or network, or may be performed via a recording medium. Further, the control device 2 is a PC for analyzing the data acquired by the transmission electron microscope 1, and a focus changing unit 21 and a hypothetical data calculating unit 22 are stored in the memory as programs corresponding to the respective functions executed by the processor.

[0017] The focus changing unit 21 changes the focal position with respect to the amplitude and phase of the electron wave. The hypothetical data calculating unit 22 individually hypothesizes the amplitude and phase of the electron waves derived from each layer, and corrects the data obtained by overlapping the individual hypothetical data of the amplitude and phase while comparing it with the experimental data actually acquired by the camera 11. The specific analysis method by the focus changing unit 21 and the hypothetical data calculating unit 22 will be described later with reference to FIG. 6.

[0018] FIG. 2 is an example of a screen output to the display device when setting the incident angle and incident direction of the electron beam. The user inputs the tilt interval, tilt start angle, and tilt end angle of the electron beam 3 when observing the sample 40 to the electron beam tilt angle setting unit 17, and inputs the tilt direction of the electron beam 3 when observing the sample 40 to the electron beam tilt direction setting unit 18. When the user finishes inputting to each setting unit and operates the start button 19, the control PC 15 of the transmission electron microscope 1 starts the measurement.

[0019] Here, when the electron beam 3 is tilted, aberration, the change of the electron beam 3 with respect to the electron biprism 8, and other changes in the electron beam path occur. Therefore, the transmission electron microscope 1 is also equipped with a function to correct these. As a correction method, optimal adjustment values are registered in advance for each tilt condition of the electron beam 3. When the tilt condition during measurement matches the registered one during measurement, it is conceivable to read the optimal adjustment value and control the transmission electron microscope 1. In this correction method, when it does not match the registered tilt condition, the optimal adjustment value is calculated by an approximation function or machine learning based on the registered tilt condition and its optimal adjustment value, and the transmission electron microscope 1 is controlled. Note that the correction method is not limited to this method.

[0020] FIG. 3 is a flowchart showing the processing in the transmission electron microscope during measurement. FIG. 4 is a schematic cross-sectional view showing how the electron beam passes through the diaphragm-type holder. FIG. 5 is a schematic cross-sectional view showing how the electron beam passes through the diaphragm-type holder when the electron beam is tilted.

[0021] When the setting of the incident angle and incident direction of the electron beam 3 is completed, the measurement is started. Then, the control PC 15 controls the deflector 6 to deflect the electron beam 3 to a predetermined incident angle and incident direction, and deflects the electron beam 3 to pass through the first layer, the second layer, and the third layer in this order, and the control PC 15 acquires the hologram image at the focal position 43 during measurement by the camera 11. Note that the focal position 43 during measurement is set within 100 μm from the position of the sample 40 to be observed.

[0022] Thereafter, the control PC 15 controls the deflector 6 to change the incident angle or incident direction of the electron beam 3 (see the tilted electron beam 31 in FIG. 5), and again deflects the electron beam 3 to pass through the first layer, the second layer, and the third layer in this order, and the control PC 15 acquires the hologram image at the focal position 43 during measurement by the camera 11. The control PC 15 repeats such measurements. When the predetermined number of measurement times is reached, the measurement is terminated, and a plurality of hologram images with different incident angles are stored in the storage unit of the control PC 15.

[0023] Next, we will explain the basic principles of an analysis method for separating electron wave information originating from each layer from electron wave information acquired by a microscope after passing through multiple layers, including the sample 40. In this example, the amplitude and phase of the electron wave information originating from each layer are separated from the electron wave information focused on the third layer (second film 42) using an electron tomography analysis algorithm. It is assumed that the electron wave is subjected to a gradual phase change that spreads from the three layers, namely the first film 41, the sample 40, and the second film 42, to the surrounding area. To simplify the model, we also assume that the first film 41, the sample 40, and the second film 42 are thin phase objects with no thickness (which only impart a phase change to the electron wave passing through them).

[0024] First, the amplitude will be described. The amplitude information on the second membrane 42 is expressed as Ψ L amp Then, since there is no information propagation in the second membrane 42, Ψ L amp = 1. Moreover, the amplitude information of the electron wave observed in the second film 42 is Ψ obsL amp =Ψ U>S>L amp ×Ψ S>L amp Here, Ψ U>S>L amp is amplitude information about the electron wave that has passed through the first film 41 and the sample 40 and propagated to the second film 42, and Ψ S>L amp is amplitude information about the electron wave that has passed through the sample 40 and propagated to the second film 42. U>S>L amp is expressed as exp(-dU) using the amplitude change coefficient dU when the electron beam 3 passes through the first film 41, and Ψ S>L amp can be approximated as exp(-dS) using the amplitude change coefficient dS when the electron beam 3 passes through the sample 40. Therefore, the amplitude information of the electron wave in the second film 42 is obsL amp =exp{-(dU+dS)}.

[0025] Next, the phase will be described. The phase information of the electron wave observed in the second film 42 is expressed as Ψ obsLphase = Ψ U>S>L phase + Ψ S>L phase + Ψ L phase can be expressed as follows. Here, Ψ U>S>L phase is the phase information regarding the electron wave that has passed through the first film 41 and the sample 40 and propagated to the second film 42, Ψ S>L phase is the phase information regarding the electron wave that has passed through the sample 40 and propagated to the second film 42, Ψ L phase is the phase information in the second film 42.

[0026] Thus, the amplitude and phase of the electron wave observed in the second film 42 can be expressed in the form of the sum of the amplitude change coefficients and the projection directions of the phase information derived from each layer. Therefore, in this embodiment, while changing the incident angle of the electron beam 3 to obtain a plurality of projection images, the amplitude change coefficients and the phase information derived from each layer are calculated using the algorithm of electron beam tomography for reconstructing the three-dimensional structure.

[0027] Hereinafter, an algorithm for separating the amplitude and phase of the electron wave derived from each layer (particularly the sample 40 which is the second layer) will be specifically described with reference to FIG. 6. FIG. 6 is a flowchart showing the processing in the control device during analysis.

[0028] First, the control device 2 acquires the hologram images for each incident angle stored in the storage unit of the control PC 15 of the transmission electron microscope 1, and reproduces the amplitude information and the phase information. Further, the focus position changing unit of the control device 2 changes the focus position to the second film 42 for the reproduced amplitude information Ψ obs amp and the phase information Ψ obs to obtain the amplitude information Ψ obsL amp and the phase information Ψ obsL phase That is, regarding the image focused on the second film 42, the amplitude change coefficient (dU + dS) = -log Ψ obsL amp and the phase information Ψ obsL phaseThe experimental data are obtained for each incident angle.

[0029] Next, the hypothetical data calculation unit 22 of the control device 2 individually hypothesizes the amplitude change coefficient and phase information of the electron waves derived from each layer. The individual hypothetical data of the amplitude change coefficient and phase information of the electron wave derived from the first film 41 are dU’ and Ψ’ respectively U>S>L phase , and the individual hypothetical data of the amplitude change coefficient and phase information of the electron wave derived from the sample 40 are dS’ and phase information Ψ’ respectively S>L phase The individual hypothetical data of the phase information of the electron wave derived from the second film 42 is Ψ’ L phase Let them be. Note that for the initial values of the individual hypothetical data, for example, the amplitude change coefficient (dU + dS) = -logΨ obtained as experimental data obsL amp and the phase information Ψ obsL phase obtained by back projection can be considered, but other than back projection can also be used. Then, the hypothetical data calculation unit 22 overlaps the individual hypothetical data to calculate the amplitude change coefficient (dU’ + dS’) and phase information Ψ’ of the electron wave in the second film 42 obsL phase That is, for the image focused on the second film 42, the hypothetical data of the amplitude change coefficient (dU’ + dS’) and phase information Ψ’ obsL phase are obtained for each incident angle.

[0030] Furthermore, the hypothetical data calculation unit 22 corrects the individual hypothetical data by comparing the hypothetical data with the experimental data. More specifically, the hypothetical data calculation unit 22 calculates the difference (error) between (dU + dS) and (dU’ + dS’) for each incident angle for the amplitude change coefficient, and for the phase information, Ψ obsL phase and Ψ’ obsL phaseThe difference (error) between the individual assumed data and the experimental data is calculated for each incident angle. Then, the assumed data calculation unit 22 determines whether the sum of the differences for each incident angle is equal to or less than a predetermined threshold. If the sum of the differences exceeds the threshold, the assumed data calculation unit 22 corrects the individual assumed data, calculates the assumed data again, and determines whether the sum of the differences from the experimental data is equal to or less than a predetermined threshold. Thereafter, the same process is repeated until the sum of the differences becomes equal to or less than the predetermined threshold. Note that instead of the sum of the differences, the average of the differences or the like may be used for the determination.

[0031] If it is determined that the sum of the differences is equal to or less than a predetermined threshold, the assumption data calculation unit 22 regards the individual assumption data at that time as the amplitude change coefficient and phase information of the electron wave originating from each layer. Among the information of the electron wave originating from each layer obtained in this way, the information of the electron wave originating from the sample 40 to be observed is particularly necessary. Then, the amplitude information Ψ of the electron wave originating from the sample 40 S>L amp can be calculated based on the amplitude change coefficient dS. However, the amplitude information Ψ S>L amp and phase information Ψ S>L phase is in a state where the focus is on the second film 42. Therefore, the focus changing unit 21 of the control device 2 uses amplitude information Ψ of the electron wave originating from the sample 40. S>L amp and phase information Ψ S>L phase , the focal position is changed from the second film 42 to the sample 40. This separates and removes the electron waves originating from the first film 41 and the second film 42, and the original amplitude information Ψ of the sample 40 is obtained. S amp and phase information Ψ S phase can be obtained with high precision, and the image quality of the sample 40 is improved. [Example]

[0032] Example 2 is an example of separating the amplitudes and phases of the electron wave information from each layer by machine learning from the electron wave information focused on the third layer (second film 42). In this example, learning is performed in advance on the amplitudes and phases of the electron waves derived from the three layers with respect to the hologram image for each incident angle, and a learning model is generated. Then, when the control device 2 acquires an actual hologram image from the transmission electron microscope 1, it outputs the amplitudes and phases of the electron waves derived from the three layers based on the learning model. Note that unsupervised learning may be used for the machine learning.

Example

[0033] In the above-described Examples 1 and 2, when the electron beam 3 was incident on the three layers composed of the first film 41, the sample 40, and the second film 42, the amplitudes and phases of the electron waves derived from each layer were calculated. However, in Example 3, when the electron beam 3 is incident on two layers, the amplitudes and phases of the electron waves derived from each layer are calculated. Here, it will be described assuming that the first layer is the sample 40 and the second layer on the downstream side (lower side) thereof is a film, but the first layer may be a film and the second layer on the downstream side (lower side) thereof may be the sample 40.

[0034] The control device 2 acquires a hologram image for each incident angle from the transmission electron microscope 1, and when reproducing the amplitude information Ψ obs amp and the phase information Ψ obs phase the focus position changing unit changes the focus position to the film, and obtains the amplitude information Ψ obsL amp (amplitude change coefficient dS) and the phase information Ψ obsL phase as experimental data. Further, the hypothetical data calculation unit 22 of the control device 2 individually hypothesizes the amplitudes (amplitude change coefficients) and phases of the electron waves derived from each layer based on the amplitude information Ψ obsL amp (amplitude change coefficient dS) and the phase information Ψ obsL phase and superimposes them to obtain the amplitude information Ψ’ obsL amp (amplitude change coefficient dS’) and the phase information Ψ’ obsLphase is obtained. Further, the hypothetical data calculation unit 22 corrects the individual hypothetical data by comparing the experimental data and the hypothetical data, and the amplitude information Ψ of the electron wave derived from the sample 40 S>L amp and the phase information Ψ S>L phase are obtained. Thereafter, the focal position changing unit changes the focal position from the film to the sample 40 with respect to the amplitude information Ψ S>L amp and the phase information Ψ S>L phase Thereby, the electron wave derived from the film is separated and removed, and the original amplitude information Ψ of the sample 40 S amp and the phase information Ψ S phase can be obtained with high precision, and the image quality of the sample 40 is improved.

[0035] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, in each of the above-described embodiments, the control device 2 which is an analysis PC is provided separately from the control PC 15 of the transmission electron microscope 1, but the analysis PC and the control PC 15 may be integrated and provided in the transmission electron microscope 1. Further, in each of the above-described embodiments, the correction of the individual hypothetical data is terminated when the total difference between the experimental data and the hypothetical data becomes equal to or less than a predetermined threshold value, but the correction may be performed a predetermined number of times or more, and the individual hypothetical data when the difference becomes minimum among them may be adopted.

[0036] Furthermore, the above-described embodiments are illustrated for easy understanding and explanation of the present invention, and are not necessarily limited to those having all the configurations described. Also, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Also, it is possible to add, delete, or replace other configurations for a part of the configuration of each embodiment.

Explanation of Reference Numerals

[0037] 1... Transmission electron microscope, 2... Control device, 3... Electron beam, 4... Electron source, 5... Condenser lens, 6... Deflector, 7... Objective lens, 8... Electron beam biprism, 9... Imaging lens system, 10... Fluorescent plate, 11... Camera, 12... Goniometer, 13... Sample holder, 14... Diaphragm-type holder, 15... Control PC, 16... Display device, 17... Electron beam tilt angle setting unit, 18... Electron beam tilt direction setting unit, 19... Start button, 21... Focus change unit, 22... Hypothetical data calculation unit, 31... Tilted electron beam, 40... Sample, 41... First film, 42... Second film, 43... Focus position

Claims

In a microscope system comprising a microscope and a control device, the microscope includes an electron source that emits an electron beam, a deflector that deflects the electron beam, a holding unit that holds a first layer, a second layer, and a third layer, and an imaging unit that acquires a hologram image of the electron beam transmitted through the first layer, the second layer, and the third layer in this order, the control device includes a focus changing unit that changes the focus position to the third layer with respect to the amplitude and phase corresponding to the hologram image for each incident angle acquired by the imaging unit, a hypothetical data calculation unit that individually assumes the amplitude and phase of the electron waves derived from each layer, and calculates, for each incident angle, hypothetical data of the amplitude and phase with the focus position at the third layer by overlapping the individually assumed amplitude and phase data, the microscope system, wherein the hypothetical data calculation unit corrects the individually assumed data by comparing the hypothetical data for each incident angle with the experimental data for each incident angle obtained by the focus changing unit.

2. In the microscope system according to claim 1, the first layer is a first film, the second layer is a sample, and the third layer is a second film, the focus changing unit changes the focus position from the second film to the sample with respect to the amplitude and phase of the electron wave derived from the sample among the individually assumed data corrected by the hypothetical data calculation unit.

3. In a microscope system comprising a microscope and a control device, the microscope includes an electron source that emits an electron beam, a deflector that deflects the electron beam, a holding unit that holds a first layer and a second layer, and an imaging unit that acquires a hologram image of the electron beam transmitted through the first layer and the second layer in this order, the control device includes a focus changing unit that changes the focus position to the second layer with respect to the amplitude and phase corresponding to the hologram image for each incident angle acquired by the imaging unit, a hypothetical data calculation unit that individually assumes the amplitude and phase of the electron waves derived from each layer, and calculates, for each incident angle, hypothetical data of the amplitude and phase with the focus position at the second layer by overlapping the individually assumed amplitude and phase data, the microscope system, wherein the hypothetical data calculation unit corrects the individually assumed data by comparing the hypothetical data for each incident angle with the experimental data for each incident angle obtained by the focus changing unit.

4. In a microscope system comprising a microscope and a control device, The microscope includes: an electron source that emits an electron beam; a deflector that deflects the electron beam; a holding unit that holds a first layer and a second layer; an imaging unit that acquires a hologram image of the electron beam transmitted through the first layer and the second layer in this order; and the control device includes: a focus changing unit that changes the focus position to the first layer with respect to the amplitude and phase corresponding to the hologram image for each incident angle acquired by the imaging unit; a hypothetical data calculation unit that individually assumes the amplitude and phase of the electron wave derived from each layer, and calculates hypothetical data of the amplitude and phase with the focus position at the first layer for each incident angle by superimposing the individually assumed amplitude and phase data; and the microscope system is characterized in that the hypothetical data calculation unit corrects the individual hypothetical data by comparing the hypothetical data for each incident angle with the experimental data for each incident angle obtained by the focus changing unit.

Images