WO2017170554A1

WO2017170554A1 - Phase-difference scanning transmission electron microscope

Info

Publication number: WO2017170554A1
Application number: PCT/JP2017/012647
Authority: WO
Inventors: 幸則永谷
Original assignee: 大学共同利用機関法人自然科学研究機構
Priority date: 2016-03-30
Filing date: 2017-03-28
Publication date: 2017-10-05
Also published as: JP6842718B2; JPWO2017170554A1

Abstract

[Problem] To provide a phase-difference scanning transmission electron microscope that has excellent operatability and that is capable of imaging the phase change of a sample with desired contrast while minimizing the electron beam exposure of the sample. [Solution] This phase-difference scanning transmission electron microscope is provided with: an electron gun 31; an irradiation optical system 32; a scan coil 33; a convergence optical system 34; an objective lens 35; and a bright field detector 36 that detects the intensity of an electron beam. A Fresnel zone plate 40 is arranged on the upstream side of a STEM focal plane such that the focus thereof is set on the STEM focal plane. Thus, electron beams including a reference wave and a main probe wave from the plate irradiate a sample object 50 placed between the convergence optical system 34 and the objective lens 35.

Description

Phase difference scanning transmission electron microscope

The present invention relates to a transmission electron microscope apparatus, and more particularly to a phase-difference scanning transmission electron microscope apparatus (Scanning Transmission Electron Microscope: STEM) that scans an electron beam and observes a sample using a phase plate.

Transmission electron microscopes are widely used for observing the nanometer structure of a thin sample. This is done by irradiating a sample with an electron beam and enlarging and projecting the electron beam transmitted through the sample onto a detector. This is a technique for seeing through the structure inside the sample, and a projection image reflecting the absorbance of the electron beam inside the sample object is obtained. For example, it is already known from Patent Document 1 below.

In such a transmission electron microscope, in particular, when the target is unstained soft tissue or resin that absorbs less electron beam and is difficult to contrast, the phase of the electron beam transmitted through the sample object is converted into contrast. So-called phase-contrast electron microscopy and phase-contrast scanning transmission electron microscopy are used. In general, a so-called scanning transmission electron microscope apparatus that observes a sample to be inspected while scanning an electron beam emitted from an electron gun is already known, for example, from Patent Document 2 below. Yes.

JP 2012-3843 A JP 2012-43563 A

The present invention includes, among the above-described phase-contrast electron microscopy and phase-contrast scanning transmission electron microscopy, because there is no transmission electron beam absorber between the sample and the detector because of its configuration. The present invention relates to a phase-difference scanning transmission electron microscope that is advantageous for reducing electron beam exposure.

By the way, also in the scanning transmission electron microscopy related to the present invention, the heavier elements present in the sample object at a higher density, the more the electron beam is scattered and a clearer contrast is obtained. This is due to the principle of absorption contrast. However, when an unstained living tissue or resin mainly composed of the same kind of light element is used as a target, there is a drawback in that it is difficult to contrast the image.

Conventionally, as a technique for solving this problem, a phase difference electron microscope method (FIG. 11) is used, which will be described in detail below, in which the phase of an electron beam transmitted through a sample object is converted into contrast using a phase plate and observed. Reference) is used. As such a phase plate, a carbon thin film type Zernike phase plate having a hole with a diameter of several hundred nm in the center of an amorphous carbon thin film having a thickness of several tens of nanometers, an amorphous carbon thin film as it is, and electron beam spot irradiation There have been proposed a holeless carbon thin film type Zernike phase plate that uses the change in physical properties of the carbon thin film due to phase change for phase modulation, an Einzel lens type that generates a potential difference only at the center by silicon micromachining technology.

However, since these phase plates are placed in the vicinity of a strong electron beam spot on the focal plane, the physical properties of the phase plate change over time due to electron beam irradiation. As a result, there is a drawback that the phase contrast is not reproduced correctly, which is recognized as a charging phenomenon of the phase plate. Further, these phase plates are easily destroyed when exposed to a strong electron beam during operation of the apparatus.

In addition, these phase plates have the side effect of absorbing the electron beam in addition to the original function of modulating the phase, and part of the electron beam transmitted through the sample is wasted. As a problem, there is a problem of increasing the electron beam exposure of the sample.

The present invention has been made in view of the circumstances in the above-described prior art, and the purpose thereof is to allow exposure of an electron beam of a smaller number of samples and to visualize a good document with a desired selectable contrast. An object of the present invention is to provide a phase difference transmission electron microscope apparatus that is excellent in operability.

To achieve the above object, according to the present invention, first, an electron gun, a converging optical system for converging an electron beam emitted from the electron gun, and an electron beam from the converging optical system with respect to a sample Scanning means for deflecting so as to scan in the horizontal direction, an objective lens for irradiating the sample with the electron beam deflected by the scanning means, and means for detecting the intensity of the electron beam transmitted through the sample In the scanning transmission electron microscope apparatus, a beam splitter is disposed between the electron gun and a converging optical system, and demultiplexes the electron beam emitted from the electron gun into a main probe wave and a reference wave at a preset ratio. A phase difference scanning transmission electron microscope apparatus is provided.

Further, according to the present invention, in the scanning transmission electron microscope apparatus described above, the intensity ratio between the main probe wave and the reference wave converted by the beam splitter is 1: 1 or a ratio close thereto (1: 4). It is preferable that ˜1: 0.25 = 0.25 or more and 4 or less, and it is preferable that the beam splitter includes a Fresnel zone plate. Further, the Fresnel zone plate demultiplexes the electron beam into at least two beams, passes one of them as the main probe wave, and converges or diverges the other as the reference wave, and In the Fresnel zone plate, the position where the converging reference wave is focused or the position where the diverging reference wave is focused by the lens system coincides with the focal point of the objective lens on the electron gun side. May be arranged.

Further, one or more lenses are disposed between the Fresnel zone plate and the objective lens, and a focal position formed by the Fresnel zone plate coincides with a focal point on the electron gun side of the objective lens. You may arrange | position so that it may move or forward.

Further, the Fresnel zone plate has a function of demultiplexing into the main probe wave passing therethrough and a reference wave to be diverged (in a spreading direction), and includes at least one lens for converging the diverging reference wave. Thus, an arrangement may be adopted in which the convergence point of the reference wave coincides with the focal point of the objective lens on the electron gun side.

The Fresnel zone plate is made of tungsten, platinum, gold, silver, copper, lead, iron, zinc, tin, molybdenum that absorbs an electron beam on a thin film made of silicon nitride, amorphous carbon, or graphene. It is preferable that it is composed of at least one or more concentric ring zones made of pure metal containing titanium, nickel or aluminum, or an alloy thereof.

In addition, the Fresnel zone plate is made of pure metal containing tungsten, platinum, gold, silver, copper, lead, iron, zinc, tin, molybdenum, titanium, nickel or aluminum, or an alloy thereof, which absorbs an electron beam. It may be a thin film composed of at least one or more concentric ring zones having a bridging portion.

The Fresnel zone plate is a phase type in which at least one or more concentric annular grooves for shifting the phase of an electron beam are formed on a thin film made of silicon nitride, amorphous carbon or graphene. Fresnel zone plate.

Furthermore, the Fresnel zone plate may be a phase / amplitude composite type Fresnel zone plate that modulates both phase and amplitude. That is, the absorption type Fresnel zone plate and the phase type Fresnel zone plate may be bonded together, or on the phase type Fresnel zone plate, tungsten that absorbs an electron beam, Form at least one or more concentric ring zones made of pure metals including platinum, gold, silver, copper, lead, iron, zinc, tin, molybdenum, titanium, nickel or aluminum, or alloys thereof. You may comprise by.

According to the present invention described above, phase difference scanning transmission that images the phase change of the electron beam of the sample object while quantitatively measuring the distribution of the phase change of the electron beam while suppressing exposure of the electron beam to the sample object. An electron microscope can be provided.

1 is an overall configuration diagram of a phase difference scanning transmission electron microscope apparatus according to an embodiment of the present invention. It is a figure which shows the plane of the Fresnel zone plate of the said phase-difference scanning transmission electron microscope apparatus, and its cross section. It is a figure which shows the plane of the bridge | crosslinking type Fresnel zone plate of the said phase-difference scanning transmission electron microscope apparatus, and its cross section. FIG. 5 is a cross-sectional view showing a phase type Fresnel zone plate and a phase / amplitude composite type Fresnel zone plate as another example. It is a whole block diagram of the phase-difference scanning transmission electron microscope apparatus which becomes other embodiment (Example 2) of this invention. It is a whole block diagram of the phase difference scanning transmission electron microscope apparatus which becomes further another embodiment (Example 3) of this invention. It is a whole block diagram of the phase difference scanning transmission electron microscope apparatus which becomes further another embodiment (Example 4) of this invention. It is a whole block diagram of the phase-difference scanning transmission electron microscope apparatus which becomes further another embodiment (Example 5) of this invention. It is a whole block diagram of the phase-difference scanning transmission electron microscope apparatus which becomes further another embodiment (Example 6) of this invention. It is a figure explaining the image generation principle of phase difference STEM which uses the electron beam obtained by using a Zernike phase plate etc. in a prior art. It is a figure explaining an example of the phase-contrast electron microscope in a prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. Prior to that, basic features and concepts of the present invention will be briefly described.

(Principle of phase difference STEM image generation)
As shown in FIG. 10A, a normal STEM uses an electron beam from an electron gun as a dotted focused beam (main probe) and scans the focused beam in a direction parallel to the sample by a scanning coil. Although the absorptance at the convergence point and the differential phase inside the convergence point are visualized and observed, the (ultra) low frequency region of the phase cannot usually be visualized.

Therefore, as shown in FIG. 10B, the phase is shifted by + π / 2 or −π / 2 with respect to the dotted convergent beam (main probe) by using the above-mentioned Zernike phase plate or the like. By scanning using an electron beam on which a reference plane wave beam (reference beam) is superposed, an ultra-low frequency region of the extent of a reference wave having a radius R can be visualized.

However, if a Zernike phase plate or the like is simply inserted into the front diffraction surface of the STEM, the amplitude B of the reference wave is overwhelmingly insufficient with respect to the amplitude (A) of the main probe wave, and sufficient contrast is obtained. I found that there was no. In place of the above, for example, a slight improvement was observed by inserting a Hilbert phase plate, however, it was still insufficient, for example, it was difficult to interpret the obtained image.

More specifically, in the phase-contrast scanning transmission electron microscope, a Zernike phase plate having a perforation at the center of the phase plate is used to generate a reference wave, and the Zernike phase plate is directly inserted into the STEM focal plane. The method is used. However, in this case, the scattered wave used as the reference wave is limited to the scattered wave generated at the edge of the small-area hole at the center of the Zernike phase plate. On the other hand, the probe wave passes through the entire area of the Zernike phase plate. For this reason, the intensity of the reference wave of the scattered wave generated at the edge portion of the hole is significantly smaller than that of the probe wave that passes as it is. As a result, the contrast due to interference is reduced.

Therefore, conventionally, for example, measures such as obtaining contrast by adjusting the projection optical system and limiting the probe wave incident on the detector have been taken. As a result, the sample exposure increases.

According to the inventor's study, the contrast of an image obtained using the above-described main probe wave and reference wave can be generally expressed by the following equation.
I∝ | Ae ^iφ + Be ^{in / 2} | = A ² + B ² + 2AB sinφ (formula 1)
Here, A is the main probe amplitude, and B is the reference wave amplitude (in the sensor unit).

Furthermore, the following formula (2) is obtained by normalizing the above formula 1 with the average intensity (A ² + B ² ).
I∝1 + 2 · {(A / B) + (B / A)} ⁻¹ · sinφ (Formula 2)

That is, it can be seen that the phase contrast of the obtained image is maximized when A and B are balanced (equal). In other words, as a device that performs the same function as a phase plate inserted in the front focal plane of the STEM, the intensity ratio (B ² / A ²⁾ between the main probe that transmits the phase plate and the reference wave generated as a scattered wave thereby. ) Is a value close to 1, specifically, a desired value is selected and used within a range of 0.25 to 4, and the above-described problem can be solved.

The present invention has been achieved on the basis of the above-described findings, and will be described in detail below with reference to the accompanying drawings in the form for carrying out the present invention (hereinafter referred to as “embodiment”). . The same number is attached | subjected to the same element through the whole description of embodiment. In the following description, the various electron lenses constituting the electron microscope are actually configured by electromagnetic coils for forming an electromagnetic field. However, in the following description, in order to simplify the description, lenses are simply used. In the figure, it is shown in the same form as a normal optical lens.
<Example 1>

(Overall configuration of phase difference scanning transmission electron microscope)
FIG. 1 shows the overall configuration of a phase-difference scanning transmission electron microscope according to an embodiment (Embodiment 1) of the present invention. That is, the apparatus includes an electron gun 31, an irradiation optical system 32, a scan coil 33, a convergence. An optical system 34, an objective lens 35, and a bright field detector 36 for detecting the intensity of the electron beam are provided as detection means.

In this embodiment, a so-called Fresnel zone plate 40 as shown in FIG. 2 is used as the beam splitter for generating the main probe wave and the reference wave. The Fresnel zone plate 40 has a function of demultiplexing into a probe wave and a reference wave using an electron beam irradiated on the sample as a wave by scattering from the surface. More specifically, the zero-order scattered wave of the Fresnel zone plate 40, that is, the beam that has passed through the plate as it is becomes the main probe wave, and the component of the wave that converges as the first-order scattered wave becomes the reference wave. The Fresnel zone plate 40 is arranged and adjusted so that the focal point of the reference wave, which is the convergent wave, coincides with the STEM focal plane, as is apparent from the drawing.

On the other hand, the sample 50 is disposed on the STEM image plane.

That is, in the phase difference scanning transmission electron microscope having the above-described configuration, the electron beam emitted from the electron gun 31 is converted into parallel light by the irradiation optical system 32, and then the main probe wave is operated by the Fresnel zone plate 40. And the reference wave. After that, the main probe wave is focused on the surface of the sample 50 by the converging optical system 34, that is, becomes the main probe beam, while the reference wave is projected onto the sample 50 as a plane wave spreading in a circle. Irradiated and both pass through the sample 50. Both these beams are deflected by the scan coil 33 while keeping the beam shape, and scan the sample 50.

Both beams transmitted through the sample 50 are superimposed on the bright field detector 36, the intensity of which is detected, and then imaged together with the scanning by the scan coil 33. That is, the main probe wave transmitted through the sample and the reference wave are superimposed as a wave, and the interference intensity is detected. As a result, the intensity corresponding to the relative phase between the main probe wave transmitted through the point on the sample and the reference wave transmitted through the spread area on the sample is detected.

<Fresnel Zone Plate (FZP)>
As apparent from FIG. 2, the Fresnel zone plate 40 is a hologram made from a spherical wave and a plane wave, and the intensity ratio and phase difference between the spherical wave and the plane wave obtained thereby can be designed freely. Is possible. FIG. 2 shows a so-called sin-type FZP, which converts an incident plane wave into a combined wave of a plane wave and two spherical waves, and sets the relative phase difference between the plane wave and the spherical wave to 90 degrees. In addition, a cos type FZP having a relative phase difference of 0 degree between a plane wave and a spherical wave is known.

Further, the Fresnel zone plate 40 can be manufactured by pattern formation of a fine processing technique of semiconductor manufacturing. For example, on the surface of the disk-shaped thin film 41 made of silicon nitride (SiN), amorphous carbon or graphene, tungsten, platinum, gold, silver, copper, lead, iron, zinc, tin, molybdenum, which absorbs electrons, It can be formed by vapor-depositing at least one or more annular zones 42 concentrically using a pure metal containing titanium, nickel, or aluminum, or an alloy thereof.

Further, as shown in FIG. 3, the Fresnel zone plate 40 does not use the thin film 41 as a support film, and absorbs electrons, such as tungsten, platinum, gold, silver, copper, lead, iron, zinc, tin, molybdenum. A thin film made of a pure metal containing titanium, nickel, or aluminum, or an alloy thereof is processed into a concentric annular zone 42 ′ with a bridging portion that supports the annular zone. You can also.

2 and 3 show an example of a so-called absorption type (amplitude type) Fresnel zone plate composed of an annular zone that absorbs an electron beam. Further, FIG. As shown in FIG. 4B, a phase-type Fresnel zone plate composed of the phase-shifting annular zone 43 or a phase-shifting annular zone 43 and an absorbing annular zone 42 are combined. A composite amplitude type Fresnel zone plate may be used. Further, a relief type Fresnel zone plate whose phase or absorption amount continuously changes may be used. By adopting them, it is possible to generate a reference wave with higher accuracy and less secondary diffraction waves.

In particular, it is important that the intensity ratio of the probe wave and the reference wave generated here is arbitrarily determined by the design of the Fresnel zone plate 40. For example, by setting the intensity ratio (R) of the main probe wave and the reference wave to a value close to 1, the contrast caused by interference can be maximized. Alternatively, by preparing a plurality of Fresnel zone plates with different intensity ratios (R) in advance and selecting and using a Fresnel zone plate with a suitable intensity ratio (R). The phase change of the sample can be imaged with a desired contrast.

In addition, the Fresnel zone plate that can be actually created has not only the effect of transmitting and converging the electron beam, but also the effect of absorbing the electron beam as a side effect thereof. Due to the structure of the scanning transmission electron microscope described above, the sample object is absorbed before being irradiated, so there is no fear that the electron beam exposure amount of the sample will increase.

In the case of using an absorption type (amplitude type) Fresnel zone plate, the incident wave is split into at least three waves, a transmitted wave, a convergent wave and a divergent wave. One becomes an unnecessary beam. This unnecessary beam can be removed by inserting a pin stop type stop at the focal position of the unnecessary beam. The pin stop type diaphragm, which will be described later, is made of tungsten, platinum, gold, silver, copper, lead, iron, zinc, which absorbs electrons on the surface of a disk-shaped thin film made of silicon nitride, amorphous carbon or graphene. It can be configured by forming a circular pattern made of pure metal including tin, molybdenum, titanium, nickel, or aluminum, or an alloy thereof, or placing spherical particles. Using a combined phase / amplitude type Fresnel zone plate, the incident wave is demultiplexed into a transmitted wave and either a convergent wave or a divergent wave. It is not necessary to insert a diaphragm.
<Example 2>

FIG. 5 shows the overall configuration of a phase difference scanning transmission electron microscope according to another embodiment (Example 2) of the present invention. In the first embodiment, the entire surface of the electron beam emitted from the electron gun 31 is irradiated on the Fresnel zone plate 40, so-called FZP is shown. However, in the second embodiment, a part of the electron beam is shown. Shows a so-called partial FZP in which the Fresnel zone plate 40 is irradiated. In this case, the reference wave irradiation region obtained is determined by the reciprocal of the groove width of the outermost annular zone (see FIG. 2), so that the reference wave irradiation region can be set as appropriate.

That is, according to the phase difference scanning transmission electron microscope according to the second embodiment, a part of the electron beam radiated from the electron gun 31 is converted into a main probe wave and a reference wave, whereby an intensity ratio between them is obtained. It is possible to set (R) more freely.
<Example 3>

FIG. 6 shows the overall configuration of a phase-contrast scanning transmission electron microscope according to still another embodiment (Example 3) of the present invention. In the first embodiment, the Fresnel zone plate 40 has a function of demultiplexing into a transmitting beam that is a main probe wave and a converging beam that is a reference wave. The third embodiment has a function of demultiplexing into a transmitting beam (solid line in the figure) serving as a main probe wave and a diverging beam (dashed line in the figure) serving as a reference wave.

A beam (solid line in the figure) irradiated with an electron beam from the electron gun 31 above the Fresnel zone plate 40 to the Fresnel zone plate 40 is transmitted and converged as it is as a main probe wave. The beam demultiplexed in the direction (solid line in the figure) is output as a parallel beam and becomes a reference wave.
<Example 4>

FIG. 7 shows the overall configuration of a phase-contrast scanning transmission electron microscope according to still another embodiment (Example 4) of the present invention. In the present embodiment as well, as in the third embodiment, the Fresnel zone plate 40 has a transmitting beam (solid line in the figure) serving as a main probe wave and a diverging beam (in the figure) serving as a reference wave. And a function of branching to a broken line).

The converging electron beam is irradiated onto the Fresnel zone plate 40 by the irradiation optical system lens 32 above the Fresnel zone plate 40, and a beam (solid line in the figure) that is transmitted and converged as it is is the main probe. On the other hand, a beam (broken line in the figure) demultiplexed in the diverging direction becomes a reference wave. The reference wave demultiplexed in the direction diverged by the Fresnel zone plate 40 is also a convergent beam, but its focal position is lower than the focal position formed by the lens of the converging optical system 34. By focusing the reference wave that has moved downward to the focal point of the STEM focal plane, the sample is irradiated with the reference wave of the main probe wave and plane wave that converge, and a phase difference STEM image is obtained by the scanning function. It is done.
<Example 5>

FIG. 8 shows the overall configuration of a phase difference scanning transmission electron microscope according to still another embodiment (Embodiment 5) of the present invention. As described above, when the amplitude type zone plate is used in the configuration shown in FIG. 6 of the third embodiment, as shown in FIG. 8, in addition to the solid transmission beam and the broken reference beam, the convergence is indicated by the dotted line. There is a disadvantage that an unnecessary beam is generated. This unnecessary beam can be removed by inserting a pin stop type stop that does not transmit only the beam at the convergence point at the convergence point of the unnecessary beam.

In other words, by inserting a pin-stop-type stop accurately at the focal position of the unwanted beam, the unwanted beam is almost completely removed, but the transmitted beam and the reference beam are hardly affected. Probe beam is generated.
<Example 6>

Furthermore, FIG. 9 shows the overall configuration of a phase-contrast scanning transmission electron microscope according to still another embodiment (Example 6) of the present invention. As described above, when the amplitude type zone plate is used in the configuration shown in FIG. 7 of the fourth embodiment, as shown in FIG. 9, in addition to the solid transmission beam and the broken reference beam, the convergence is indicated by the dotted line. There is a disadvantage that an unnecessary beam is generated.

However, this unnecessary beam can be removed in the same manner as in the fifth embodiment shown in FIG. 8 by inserting a pin stop type stop at the convergence point of the unnecessary beam.

It will be apparent to those skilled in the art that the effects similar to those of the phase difference scanning transmission electron microscopes shown in the first and second embodiments can be obtained by these third to sixth embodiments.

In all of the embodiments described above, the Fresnel zone plate can be removed and used at any time as a conventional STEM. It is also possible to easily convert a conventional STEM into a phase difference STEM by inserting a Fresnel zone plate into a diaphragm port of a conventional STEM irradiation system.

As described in detail above, in the embodiment described above, instead of the conventional Zernike phase plate inserted in the STEM focal plane at the upstream side of the STEM focal plane, as an example, a Fresnel zone plate is used. The above-mentioned problem is solved by inserting at a position where the direct focus of the zone plate or the focal point transferred or moved by the lens system comes to the STEM focal plane. That is, the present invention provides:

(1) A scanning transmission electron microscope as an alternative function of a Zernike phase plate that is disposed between an electron gun, the electron beam source, and a converging optical system and through which an electron beam emitted from the electron beam source passes. Means for detecting the intensity of an electron beam transmitted through a sample object disposed behind the objective lens using a Fresnel zone plate.

(2) In the configuration of the above (1), the Fresnel zone plate splits the electron beam into two or more beams, and one of the beams keeps an incident beam wavefront. The beam is focused on the sample by the objective lens, the other beam becomes a convergent beam, the convergence point is located at the front focal plane of the objective lens, and on the sample plane, the beam spread by the objective lens Become.

(3) In the configuration of (1), the Fresnel zone plate has a relative phase difference of zero (0), or an electron wave that passes while maintaining a wavefront, This is a positive or negative value and is a finite value including 90 degrees.

That is, in the present invention, by efficiently generating a pair of a main probe beam and a reference beam used for phase difference scanning transmission electron microscopy, a higher phase contrast, fewer electron beam exposures of a sample, a longer phase plate Technology is provided to achieve lifetime.

In the above embodiment, the phase plate that uses the Fresnel zone plate as the phase plate for converting the passing electron beam into the main probe wave and the reference wave at a desired intensity ratio has been described in detail. It will be apparent to those skilled in the art that other materials may be used as long as they exhibit similar functions.

In the foregoing, various phase difference scanning transmission electron microscope apparatuses according to embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments are described in detail for the entire system in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

The present invention relates to a transmission electron microscope apparatus widely used for observing a nanometer structure of a thin sample, and in particular, a phase-difference type scanning transmission electron that scans an electron beam and observes a sample while using a phase plate. It can be used in a microscope apparatus.

DESCRIPTION OF SYMBOLS 31 ... Electron gun, 32 ... Irradiation optical system, 33 ... Scan coil, 34 ... Convergence optical system, 35 ... Objective lens, 36 ... Bright field detector, 40 ... Fresnel zone plate, 41 ... Disc-shaped thin film, 42 ... annular zone, 42 '... freestanding annular zone, 43 ... annular zone groove, 50 ... sample.

Claims

An electron gun,
A converging optical system for converging the electron beam emitted from the electron gun;
Scanning means for deflecting the electron beam from the converging optical system so as to scan the sample in a horizontal direction;
An objective lens for irradiating the sample with the electron beam deflected by the scanning means;
In a scanning transmission electron microscope apparatus provided with a means for detecting the intensity of an electron beam transmitted through the sample,
An electron beam radiated from the electron gun, which is disposed at a position different from the front focal plane of the objective lens between the electron gun and the objective lens, is converted into a main probe wave and a reference wave having a preset ratio. A phase difference scanning transmission electron microscope apparatus comprising a beam splitter, wherein the main probe wave and the reference wave are electron waves having different focal positions.
2. The scanning transmission electron microscope apparatus according to claim 1, wherein a ratio between the main probe wave and the reference wave converted by the beam splitter is 0.25 or more and 4 or less. apparatus.
3. The scanning transmission electron microscope apparatus according to claim 2, wherein the beam splitter includes a Fresnel zone plate.
4. The scanning transmission electron microscope apparatus according to claim 3, wherein the Fresnel zone plate demultiplexes the electron beam into at least two beams, passes one of them as the main probe wave, and sets the other as the main probe wave. The objective lens converges or diverges as a reference wave, and the Fresnel zone plate has a position where the converged reference wave is focused or a position where the diverging reference wave is focused by a lens system. The phase difference scanning transmission electron microscope apparatus is arranged so as to coincide with the focal point on the electron gun side.
5. The scanning transmission electron microscope apparatus according to claim 4, wherein the Fresnel zone plate is arranged so as to demultiplex the entire electron beam.
5. The scanning transmission electron microscope apparatus according to claim 4, wherein the Fresnel zone plate is arranged so as to demultiplex a part of the electron beam. .
5. The scanning transmission electron microscope apparatus according to claim 4, wherein one or more lenses are provided between the Fresnel zone plate and the objective lens, and the lens is connected to the Fresnel zone plate. Is arranged at a position to move or transfer so as to coincide with the focal point of the objective lens on the electron gun side.
5. The scanning transmission electron microscope apparatus according to claim 4, wherein the Fresnel zone plate has a function of demultiplexing the main probe wave to pass through and the reference wave to diverge, and further diverges the reference. A position in which at least one lens for converging waves is provided, and the lens is provided so that the convergence point of the reference wave and the focal point on the electron gun side of the objective lens coincide with each other. Phase difference scanning transmission electron microscope apparatus.
4. The scanning transmission electron microscope apparatus according to claim 3, wherein the Fresnel zone plate is formed on a thin film made of silicon nitride, amorphous carbon or graphene, and absorbs an electron beam tungsten, platinum, gold, silver. A phase difference characterized by comprising at least one or more concentric annular zones made of copper, lead, iron, zinc, tin, molybdenum, titanium, nickel, aluminum, or an alloy thereof. Scanning transmission electron microscope apparatus.
4. The scanning transmission electron microscope apparatus according to claim 3, wherein the Fresnel zone plate is made of tungsten, platinum, gold, silver, copper, lead, iron, zinc, tin, molybdenum, titanium, nickel that absorbs an electron beam. Alternatively, a phase-contrast scanning transmission electron microscope apparatus characterized by being a thin film made of at least one or more concentric ring zones made of aluminum or an alloy thereof and having a bridging portion.
4. The scanning transmission electron microscope apparatus according to claim 3, wherein the Fresnel zone plate has at least one concentric circle for shifting the phase of an electron beam on a thin film made of silicon nitride, amorphous carbon, or graphene. A phase-contrast scanning transmission electron microscope apparatus comprising at least one ring-shaped groove.
10. The scanning transmission electron microscope apparatus according to claim 9, wherein the Fresnel zone plate is a concentric circle that shifts the phase of an electron beam on a thin film made of silicon nitride, amorphous carbon, or graphene. A phase-difference scanning transmission electron microscope apparatus characterized in that an absorption type Fresnel zone plate composed of at least one ring-shaped groove is bonded.
12. The scanning transmission electron microscope apparatus according to claim 11, wherein the Fresnel zone plate further includes tungsten absorbing an electron beam on a thin film made of silicon nitride, amorphous carbon, or graphene. , Platinum, gold, silver, copper, lead, iron, zinc, tin, molybdenum, titanium, nickel or aluminum, or by forming at least one concentric ring zone made of an alloy thereof A phase-contrast scanning transmission electron microscope apparatus.