JP7332803B2 - transmission electron microscope - Google Patents

Description

The present invention relates to transmission electron microscopes.

2. Description of the Related Art In recent years, transmission electron microscope image observation is generally performed by a detector (for example, a digital camera) using a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) element. The detector produces image information by converting light intensity into an electrical signal by each detector element. Therefore, transmission electron microscopes require a medium (for example, a scintillator) that converts electron beams into light. For this medium, it is important to obtain a local and high light emission amount in order to obtain image information of higher image quality.

A common scintillator material is p47 (Y2SiO5:Ce). This material emits light only from particles present in the region irradiated with the electron beam. As shown in Non-Patent Document 1, the size of these particles is about 3 μm, so local light emission is possible, and they are widely used as materials for scintillators.

A scintillator manufactured by laminating microparticles changes the amount of light emitted depending on the energy of the irradiated electron beam and the thickness of the scintillator. Since a transmission electron microscope uses an electron beam accelerated by a voltage of several hundred kilovolts to observe a sample, a scintillator with a thickness of several tens of micrometers is required, mainly in order to obtain the maximum amount of light emission at the accelerating voltage used. is generally designed to

A transmission electron microscope can change the resolution and contrast of an observation image by changing the acceleration voltage of the irradiated electron beam. A general transmission electron microscope can set a wide range of acceleration voltages from tens of kilovolts to hundreds of kilovolts. On the other hand, in general transmission electron microscopes, as described above, the thickness of the scintillator is designed so that the maximum amount of light emission can be obtained at the accelerating voltage that is mainly used. Therefore, in an acceleration voltage band deviating from the designed acceleration voltage, the light emission amount of the scintillator is low, and the quality of the observed image is deteriorated.

In view of the above problems, Patent Document 1 proposes a composite scintillator in which a crystal scintillator and a particle scintillator are combined. The composite scintillator in the document causes a crystal scintillator to emit light by electrons transmitted through a particle scintillator.

JP 2015-005351 A

N. R. Comins et al. , J. Phys. E: Sci. Instrum. , Vol. 11A. 1041-1047 (1978)

The composite scintillator described in Patent Document 1 can obtain a high amount of light emission in an acceleration voltage range in which electron beams pass through the thickness of the particle scintillator. However, in the acceleration voltage range where the electron beam does not pass through the thickness of the particle scintillator, the amount of light emitted decreases as in the conventional case.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a transmission electron microscope capable of increasing the amount of light emitted from a scintillator over a wide range of accelerating voltages.

A transmission electron microscope according to the present invention has a first scintillator having a first emission characteristic and a second scintillator having a second emission characteristic different from the first emission characteristic, and the first scintillator and the second scintillator The position of the first scintillator and the position of the second scintillator are adjusted so that only one of them receives the electron beam that has passed through the sample.

According to the transmission electron microscope according to the present invention, it is possible to photograph an observation image having a high amount of light emission over a wide range from a low acceleration voltage to a high acceleration voltage.

1 is a configuration diagram of a transmission electron microscope 100 according to Embodiment 1. FIG. Details of the essential parts of the detection system 114 are shown. The luminance values of images created by irradiating the first scintillator 109 and the second scintillator 110 with the electron beam EB are shown. 4 is a flowchart for explaining the operation flow when the transmission electron microscope 100 applies an accelerating voltage; It is an example of an image brightness value obtained by switching the first scintillator 109 and the second scintillator 110. FIG.

<Embodiment 1>
In Embodiment 1 of the present invention, one of a plurality of movable scintillators having different thicknesses of phosphor coated on the scintillator is selected according to a set acceleration voltage, and the selected scintillator is irradiated with an electron beam. Provided is a transmission electron microscope capable of photographing an observation image having a high amount of light emission in a wide range of accelerating voltage by moving it to an irradiated position.

FIG. 1 is a configuration diagram of a transmission electron microscope 100 according to the first embodiment. The transmission electron microscope 100 includes: an electron gun 103; a specimen holder 105 supporting an observation object 104; objective lens 107 for focusing; imaging lens 108 for magnifying or reducing the electron beam transmitted through observation object 104 to form an image; detection for detecting an image projected on first scintillator 109 or second scintillator 110 detector 113; detection system 114; high-voltage power supply controller 115 for applying acceleration voltage V between cathode 101 and anode 102; power source 116 for driving drive mechanism 112; computer 117 (control unit); signal transmission unit 118 for transmitting control signals from the computer 117 to each unit (for example, high voltage power supply control unit 115, power source 116); display unit 119 for outputting signals from the computer 117; Input unit 120 for inputting .

The electron gun 103 further includes a cathode 101 that emits an electron beam EB and an anode 102 that is an electrode for accelerating the electron beam EB. The detection system 114 comprises a first scintillator 109 , a second scintillator 110 , a container 111 and a drive mechanism 112 . The first scintillator 109 and the second scintillator 110 are arranged on a projection plane for projecting the imaged electron beam. The first scintillator 109 and the second scintillator 110 are arranged adjacent to each other on a horizontal plane (a plane perpendicular to the irradiation direction of the electron beam EB). The storage device 111 stores the first scintillator 109 and the second scintillator 110 . A drive mechanism 112 moves the container 111 horizontally.

FIG. 2 shows details of the essential parts of detection system 114 . The detector 113 includes: a transmission unit (for example, an optical lens) 201 that transmits the light emitted by the first scintillator 109 or the second scintillator 110; the light emitted by each scintillator is converted into an electrical signal and output as image information. image output unit 202.

Each scintillator is composed of a fluorescent material that emits light when irradiated with an electron beam. For example, P47 (Y ₂ SiO ₅ :Ce) can be used as the fluorescent material. The first scintillator 109 and the second scintillator 110 differ from each other in the thickness of the coated fluorescent material. For example, the fluorescent material applied to the first scintillator 109 has a thickness of 24 μm, and the fluorescent material applied to the second scintillator 110 has a thickness of 6 μm.

The driving mechanism 112 can be switched so that only one of the first scintillator 109 and the second scintillator 110 is positioned directly above the detector 113 . For example, when the first scintillator 109 is directly above the detector 113, the electron beam EB is projected onto the first scintillator 109, causing the first scintillator 109 to emit light. 202 converts the emitted light into image information. The same applies to the second scintillator 110 as well.

The electron gun 103 planarly irradiates the sample with an electron beam EB. The term "planar" as used herein means that a planar region having a certain area is simultaneously irradiated, instead of irradiating the entire surface of the sample by scanning the irradiation point. Therefore, the first scintillator 109 or the second scintillator 110 emits planar light. The image output unit 202 can be configured by an imaging device that captures an image of the scintillator that emits light on the surface. Thereby, a planar image of the sample can be obtained.

FIG. 3 shows luminance values of images created by irradiating the first scintillator 109 and the second scintillator 110 with the electron beam EB. The vertical axis indicates the image luminance value, and the horizontal axis indicates the acceleration voltage (kV). The setting conditions of the image output unit 202 were the same when using the first scintillator 109 and when using the second scintillator 110 . Therefore, the image luminance value is the same as the amount of light emitted by the first scintillator 109 and the second scintillator 110, respectively. That is, the first scintillator 109 and the second scintillator 110 have different emission characteristics with respect to the acceleration voltage, as shown in FIG.

Within the acceleration voltage range of the graph shown in FIG. 3, the image brightness value of the first scintillator 109 reaches its maximum value at an acceleration voltage of 120 kV, and the image brightness value decreases as the acceleration voltage decreases. On the other hand, the image brightness value of the second scintillator 110 takes the maximum value at an acceleration voltage of 40 kV, and the image brightness value decreases as the acceleration voltage increases. That is, on the acceleration voltage side higher than the intersection point A, higher image brightness can be obtained by using the first scintillator 109, and on the acceleration voltage side lower than the intersection point A, it is possible to obtain higher image brightness by using the second scintillator 110. can be obtained. At intersection point A, either can be used.

FIG. 4 is a flow chart for explaining the operation flow when the transmission electron microscope 100 applies an accelerating voltage. This flowchart is executed by the computer 117 controlling each part of the transmission electron microscope 100 . Each step in FIG. 4 will be described below.

(Fig. 4: Step S01)
The computer 117 holds in advance the threshold Vs for switching between the first scintillator 109 and the second scintillator 110 and the position P of the storage 111 as initial values. For example, the initial value of position P is P1. P1 is the position at which the electron beam EB is applied to the first scintillator 109 . These initial values may be stored in advance in a storage device included in the computer 117 or may be specified by the user via the input unit 120 .

(Fig. 4: Step S02)
The user specifies the acceleration voltage V via the input unit 120 . The computer 117 stores the acceleration voltage V input by the user in a storage area within the computer 117 .

(Fig. 4: Step S03)
Computer 117 compares threshold Vs and acceleration voltage V. FIG. When the acceleration voltage V is equal to or higher than the threshold Vs, the process proceeds to step S04. If the acceleration voltage V is less than the threshold Vs, the process proceeds to step S06.

(Fig. 4: Steps S04-S05)
The computer 117 determines whether the position P of the container 111 is P1 (S04). If not P1, a signal is transmitted to the power source 116 to change the position P of the container 111 to P1 (S05). If it is P1, the process proceeds to step S08.

(Fig. 4: Steps S06-S07)
The computer 117 determines whether the position P of the container 111 is P2 (S06). If not P2, a signal is transmitted to the power source 116 to change the position P of the container 111 to P2 (S07). If it is P2, the process proceeds to step S08.

(Fig. 4: Step S08)
Computer 117 transmits an acceleration voltage signal to high-voltage power supply controller 115 and applies acceleration voltage V to it.

(Fig. 4: Step S02: Supplement)
When changing the acceleration voltage while the acceleration voltage is being applied, the computer 117 starts this flowchart from step S02.

FIG. 5 shows an example of image luminance values obtained by switching between the first scintillator 109 and the second scintillator 110 . Here, an example having the same light emission characteristics as in FIG. 3 is shown. A high image luminance value can be obtained in a wide acceleration voltage band by making either one of the first scintillator 109 and the second scintillator 110 receive the electron beam EB with the intersection point A as a boundary.

<Embodiment 1: Summary>
The transmission electron microscope 100 according to the first embodiment includes a first scintillator 109 and a second scintillator 110 having different emission characteristics with respect to acceleration voltage, and only scintillators that can obtain a higher image luminance value at the acceleration voltage specified by the user are included. The position of each scintillator is adjusted so as to receive the electron beam EB. As a result, the light emission amount of the scintillator can be increased in a wide acceleration voltage band, and high image brightness can be obtained.

<Embodiment 2>
In Embodiment 2 of the present invention, a modified example of each part included in the transmission electron microscope 100 will be described. Since other configurations are the same as those of the first embodiment, differences from the first embodiment will be described below.

In the first embodiment, it has been described that the first scintillator 109 and the second scintillator 110 have different light emission characteristics as shown in FIG. 3 due to the different coating thicknesses of the fluorescent materials. Alternatively or in combination with the phosphor thickness, the phosphor materials may be different from each other. In other words, the first scintillator 109 and the second scintillator 110 need to be configured so that at least the light emission characteristics with respect to the acceleration voltage are different from each other, but the method of realizing the light emission characteristics is arbitrary. For example, if the first scintillator 109 has a higher image brightness value at the first acceleration voltage and the second scintillator 110 has a higher image brightness value at the second acceleration voltage, then at least the first acceleration voltage and the second acceleration voltage , it can be said that there is significance in switching between the first scintillator 109 and the second scintillator 110 .

In FIG. 3, the light emission characteristic of the first scintillator 109 rises to the right, and the light emission characteristic of the second scintillator 110 falls to the right, but the present invention is not limited to this. For example, even if both are upward-sloping to the right, if the inclinations are different, an intersection point A will occur. Similarly, both may be downward sloping. Furthermore, even if the intersection point A does not occur, if a scintillator with a high image luminance value is used at the specified acceleration voltage, the same effect as in the first embodiment can be exhibited. Furthermore, there may be a plurality of intersections of light emission characteristics. Even in this case, if a scintillator with a high image luminance value is used at the specified acceleration voltage, the same effect as in the first embodiment can be exhibited.

Although the first scintillator 109 and the second scintillator 110 are provided in the first embodiment, the number of scintillators may be three or more. That is, if the scintillators have mutually different emission characteristics with respect to acceleration voltage, the highest image luminance value can be obtained for each acceleration voltage by switching the scintillators so that only one scintillator receives the electron beam.

Although the acceleration voltage is changed after setting the position of the scintillator in the first embodiment, the same effect can be obtained by changing the position of the scintillator after changing the acceleration voltage.

The container 111 can mount two scintillators, for example, side by side in the horizontal direction, and the shape of the container 111 may be changed according to the number and thickness of the scintillators. Enclosure 111 may be capable of mounting more than two scintillators. As for the arrangement of the scintillators in the storage device 111, for example, the scintillators can be arranged in one line, or the scintillators can be arranged in a ring. Other arrangements may be used.

In Embodiment 1, the first scintillator 109 and the second scintillator 110 are arranged adjacent to each other in the horizontal direction (direction perpendicular to the irradiation direction of the electron beam EB). It does not have to be placed. For example, in FIG. 2, each scintillator may be vertically stacked in a place where the electron beam EB does not hit, and only the scintillator that receives the electron beam EB may be pushed out horizontally and thrown into the electron beam EB. However, the direction in which each scintillator is moved must be at least parallel to the irradiation direction of the electron beam EB. This is because, if each scintillator is moved parallel to the irradiation direction of the electron beam EB, the electron beam EB may simultaneously irradiate a plurality of scintillators.

When the first scintillator 109 and the second scintillator 110 are arranged adjacent to each other in the horizontal direction, the drive mechanism 112 only needs to push and pull the first scintillator 109 and the second scintillator 110 together, so the structure of the drive mechanism 112 can be simple. There are advantages. When the first scintillator 109 and the second scintillator 110 are vertically stacked (or at least partially overlapped in the vertical direction), the plane size of the light emitting member can be suppressed, but the drive mechanism 112 has a more complicated structure and operation. is required.

In the first embodiment, the electron gun 103 irradiates the sample with the electron beam EB in a plane. As a configuration having an electron optical system for scanning the irradiation point, the entire surface of the sample may be irradiated by scanning the irradiation point. In this case, the diffraction pattern of the electron beam from the sample appears on the first scintillator 109 or the second scintillator 110 . Therefore, a planar image of the sample can be obtained by synchronizing the position of the irradiated point to be scanned with the conversion result of the light emitted from the first scintillator 109 or the second scintillator 110 into image information by the image output unit 202. . As a result, even when the transmission electron microscope 100 is operated as a scanning transmission electron microscope (STEM), the light emission amount of the scintillator can be increased in a wide acceleration voltage range as in the first embodiment, resulting in high image brightness. can be obtained. Furthermore, by forming an image from an arbitrary portion of the output image from the image output unit 202, an STEM image is formed from an arbitrary scattered wave component in a state in which the light emission amount of the scintillator is increased in a wide acceleration voltage range. be able to.

100: Transmission electron microscope 109: First scintillator 110: Second scintillator 111: Container 112: Driving mechanism 113: Detector 114: Detection system 115: High voltage power supply control unit 116: Power source 117: Computer 118: Signal transmission unit 201 : Transmission unit 202: Image output unit

Claims (13)

A transmission electron microscope that acquires an image of the sample using an electron beam that has passed through the sample,
an electron gun that emits the electron beam;
a light-emitting member that converts the electron beam that has passed through the sample into light;
a driving mechanism for adjusting the position of the light emitting member;
with
The light emitting member has a first scintillator having a first light emission characteristic and a second scintillator having a second light emission characteristic different from the first light emission characteristic,
Both the first scintillator and the second scintillator are configured to be movable by the drive mechanism,
The drive mechanism adjusts the positions of the first scintillator and the second scintillator so that only one of the first scintillator and the second scintillator receives the electron beam that has passed through the sample. A transmission electron microscope characterized by: The driving mechanism moves only one of the first scintillator and the second scintillator by moving the first scintillator and the second scintillator in a direction not parallel to the electron beam irradiation direction. 2. The transmission electron microscope according to claim 1, wherein is adapted to receive the electron beam that has passed through the sample. The first scintillator and the second scintillator are arranged adjacent to each other in a direction perpendicular to the irradiation direction,
The drive mechanism moves the first scintillator and the second scintillator in a direction perpendicular to the direction of irradiation, so that only one of the first scintillator and the second scintillator moves toward the sample. 3. The transmission electron microscope according to claim 2, wherein the electron beam transmitted through the is received. The transmission electron microscope further comprises an electrode that applies an accelerating voltage to the electron beam,
The first light emission characteristic is a characteristic of emitting light with a first light emission amount when the acceleration voltage is a first voltage value,
The second light emission characteristic is a characteristic of emitting light with a second light emission amount different from the first light emission amount when the acceleration voltage is the first voltage value,
2. The transmission electron microscope according to claim 1, wherein said driving mechanism switches between said first scintillator and said second scintillator to receive said electron beam according to the set value of said accelerating voltage. The second light emission amount is a value smaller than the first light emission amount,
The drive mechanism adjusts the position of the first scintillator and the position of the second scintillator so that only the first scintillator receives the electron beam when the acceleration voltage is the first voltage value. 5. The transmission electron microscope according to claim 4, characterized by: The first light emission characteristic is a characteristic of emitting light with a third light emission amount smaller than the first light emission amount when the acceleration voltage is a second voltage value smaller than the first voltage value,
The second light emission characteristic is a characteristic of emitting light with a fourth light emission amount larger than the second light emission amount when the acceleration voltage is the second voltage value,
5. The transmission electron microscope according to claim 4, wherein the drive mechanism switches between the first scintillator and the second scintillator to receive the electron beam according to the set value of the acceleration voltage. The fourth light emission amount is a value larger than the third light emission amount,
The drive mechanism adjusts the position of the first scintillator and the position of the second scintillator so that only the second scintillator receives the electron beam when the acceleration voltage is the second voltage value. 7. The transmission electron microscope according to claim 6, characterized by: The second light emission amount is a value smaller than the first light emission amount,
The first light emission characteristic and the second light emission characteristic are characteristics that give the same amount of light emission when the acceleration voltage is a third voltage value that is lower than the first voltage value and higher than the second voltage value,
The drive mechanism adjusts the positions of the first scintillator and the second scintillator so that only the first scintillator receives the electron beam when the acceleration voltage is higher than the third voltage value. ,
The drive mechanism adjusts the positions of the first scintillator and the second scintillator so that only the second scintillator receives the electron beam when the acceleration voltage is smaller than the third voltage value. 7. A transmission electron microscope according to claim 6, characterized in that: The light emitting member further has a third scintillator having a third light emission characteristic different from the first light emission characteristic and the second light emission characteristic,
The drive mechanism positions the first scintillator and the third scintillator so that only one of the first scintillator, the second scintillator, and the third scintillator receives the electron beam that has passed through the sample. 2. The transmission electron microscope according to claim 1, wherein the positions of the second scintillator and the position of the third scintillator are adjusted. The first scintillator is configured to have the first light emission characteristic by being coated with a phosphor having a first thickness,
2. The second scintillator according to claim 1, wherein the second scintillator is coated with a phosphor having a second thickness different from the first thickness, so that the second scintillator has the second light emission characteristic. transmission electron microscope. The first scintillator is configured to have the first light emission characteristic by being coated with a phosphor of a first material,
2. The second scintillator according to claim 1, wherein the second scintillator is coated with a phosphor made of a second material different from the first material, so that the second scintillator has the second light emission characteristic. Transmission electron microscope. The electron gun planarly irradiates the electron beam onto the sample,
2. The transmission electron microscope according to claim 1, further comprising an imaging device for imaging the light-emitting member that has received the planar electron beam. The electron gun irradiates the sample with the electron beam in a point-like manner,
The transmission electron microscope further includes:
an electron optical system for scanning the irradiation point of the electron beam on the surface of the sample;
an imaging device for imaging the light-emitting member that has received the dot-like electron beam;
The transmission electron microscope of claim 1, comprising:

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