透镜系统 - 版本历史

Li.qun：/* 36-3. condenser-objective lens (C-O lens) */

2020-08-21T03:22:23Z

‎36-3. condenser-objective lens (C-O lens)

Li.qun：/* 36-3. condenser-objective lens (C-O lens) */

2020-08-21T03:22:06Z

‎36-3. condenser-objective lens (C-O lens)

Li.qun：/* 36-3. condenser-objective lens (C-O lens) */

2020-08-21T03:20:05Z

‎36-3. condenser-objective lens (C-O lens)

Li.qun：/* 36-3. condenser-objective lens (C-O lens) */

2020-08-21T03:18:45Z

‎36-3. condenser-objective lens (C-O lens)

Li.qun：/* 55-2. objective lens */

2020-07-29T02:06:57Z

‎55-2. objective lens

Li.qun：/* 55-2. objective lens */

2020-07-29T02:05:21Z

‎55-2. objective lens

2020年7月2日 (四) 03:13 Li.qun

2020-07-02T03:13:41Z

Li.qun：/* 13. diffraction limit */

2020-05-27T01:47:10Z

‎13. diffraction limit

Li.qun：/* 13. diffraction limit */

2020-05-27T01:46:56Z

‎13. diffraction limit

Li.qun：/* 13. diffraction limit */

2020-05-27T01:45:34Z

‎13. diffraction limit

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 For observation of the TEM image including a HREM image (atomic level resolution image), parallel beam illumination onto a specimen is required. To produce the parallel beam, a condenser mini lens is used to converge the incident beam onto the focal point of the pre-magnetic field of the C-O lens (right of Fig. 3). The electron beam passing through the specimen is enlarged by the post-magnetic field of the C-O lens and further enlarged with intermediate and projector lenses, and finally a TEM image is formed on the screen.
 [[文件:C-O lens.jpg]]
 [[文件:C-O lens-3.jpg]]
 <pre>Related term

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 For observation of the TEM image including a HREM image (atomic level resolution image), parallel beam illumination onto a specimen is required. To produce the parallel beam, a condenser mini lens is used to converge the incident beam onto the focal point of the pre-magnetic field of the C-O lens (right of Fig. 3). The electron beam passing through the specimen is enlarged by the post-magnetic field of the C-O lens and further enlarged with intermediate and projector lenses, and finally a TEM image is formed on the screen.
 [[文件:C-O lens.jpg]]
+[[文件:C-O lens-3.jpg]]
 <pre>Related term
 condenser mini lens</pre>

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 Demagnification of the incident beam by the C-O lens is essential for obtaining a high resolution of the STEM image, sub-nanometer-area illumination for CBED and for decreasing the analysis area (sub-nanometer-size) of EDS and EELS. The post-magnetic field (second lens) produces an enlarged image of the focused beam on the specimen.
 For observation of the TEM image including a HREM image (atomic level resolution image), parallel beam illumination onto a specimen is required. To produce the parallel beam, a condenser mini lens is used to converge the incident beam onto the focal point of the pre-magnetic field of the C-O lens (right of Fig. 3). The electron beam passing through the specimen is enlarged by the post-magnetic field of the C-O lens and further enlarged with intermediate and projector lenses, and finally a TEM image is formed on the screen.
 <pre>Related term

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 condenser-objective lens (C-O lens), condenser lens, objective mini lens, scanning transmission electron microscope (STEM) image, convergent-beam electron diffraction, CBED, high-resolution electron microscopy, HREM</pre>
 ===36-3. condenser-objective lens (C-O lens)===
-The "condenser-objective lens (C-O lens)" makes the pre-magnetic field of the objective lens act as a condenser lens so that the electron beam is focused onto the specimen, and makes the post-magnetic field act as an objective lens to form the specimen image at the image plane. Since the electron beam is demagnfied to ～1/100 by the pre-magnetic field on the specimen, the C-O lens is essential for various purposes, such as CBED that requires sub-nanometer-area illumination, improvement of STEM image resolution, and decreasing of analysis region for EDS and EELS. To produce a parallel beam for HREM in the TEM mode, a condenser mini lens is used.
+The condenser-objective lens (C-O lens) makes its pre-magnetic field act as a condenser lens for the electron beam to be focused onto a specimen, and makes its post-magnetic field act as an objective lens to form the specimen image on the image plane.
 <pre>Related term
 condenser mini lens</pre>
 ==37. combination aberration==
 If two thin optical elements (lenses, multi-poles, etc.) are placed at a free space, higher order aberrations than those inherent to the elements can arise due to a synergetic effect of the inherent aberrations. The higher order aberrations induced are called "combination aberrations." A thick hexapole spherical aberration corrector produces a third-order negative spherical aberration by a self-conbination effect of two three-fold astigmatism fields (second-order aberration). With the use of this third-order negative spherical aberration, the third-order positive aberration of the objective lens can be corrected. In the case of the combination between a spherical aberration (Cs) corrector and an objective lens with a free space (incomplete image transfer) between them, a positive or negative fifth-order spherical aberration is induced by a cross combination between the third-order negative aberration of the Cs corrector and the third-order positive aberration of the objective lens. Using the fifth-order spherical aberration produced, the residual fifth-order spherical aberration of the system can be removed.

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 ===55-2. objective lens===
 The "objective lens" is the first-stage lens to form an image using electrons exiting from the specimen. The objective lens is the most important lens in the imaging lens system because the performance of this lens determines the image quality (resolution, contrast, etc). A good objective lens has both a small spherical aberration (Cs) coefficient and a small chromatic aberration (Cc) coefficient. To decrease these coefficients, shortening the distance between the two magnetic poles and decreasing the bore diameter of the polepiece and are required. Since the side-entry-type specimen holder is inserted between the two magnetic poles, there is a limitation on shortening the distance. For the top-entry-type specimen holder, an asymmetric polepiece whose upper bore diameter is larger than that of the lower one is used.
 Fig. The objective lens consists of a polepiece to determine the magnetic-field of the lens, a yoke to create a magnetic path, and a copper wire coil. The coil is wound in the yoke around the circumference of the optical axis. A magnetic field is generated by the electric current passing through the coil and a magnetic flux is generated in the yoke. Then, a leakage magnetic field is created in vacuum from the polepiece attached to the end of the yoke. The polepiece of the lens is made of a magnetic component and has a gap to create a leakage magnetic field. As is seen in Figure, the polepiece is cylindrically symmetric and an electron beam passes through the center of the polepiece.

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 ===55-2. objective lens===
-The "objective lens" is the first-stage lens to form an image using electrons exiting from the specimen. The objective lens is the most important lens in the imaging lens system because the performance of this lens determines the image quality (resolution, contrast, etc). A good objective lens has both a small spherical aberration (Cs) coefficient and a small chromatic aberration (Cc) coefficient. To decrease these coefficients, shortening the distance between the two magnetic poles and decreasing the bore diameter of the polepiece and are required. Since the side-entry-type specimen holder is inserted between the two magnetic poles, there is a limitation on shortening the distance. For the top-entry-type specimen holder, an asymmetric popiece whose upper bore diameter is larger than that of the lower one is used.
+The "objective lens" is the first-stage lens to form an image using electrons exiting from the specimen. The objective lens is the most important lens in the imaging lens system because the performance of this lens determines the image quality (resolution, contrast, etc). A good objective lens has both a small spherical aberration (Cs) coefficient and a small chromatic aberration (Cc) coefficient. To decrease these coefficients, shortening the distance between the two magnetic poles and decreasing the bore diameter of the polepiece and are required. Since the side-entry-type specimen holder is inserted between the two magnetic poles, there is a limitation on shortening the distance. For the top-entry-type specimen holder, an asymmetric polepiece whose upper bore diameter is larger than that of the lower one is used.
 <pre>Related term
 ultra-high-resolution polepiece, multiuse polepiece, high-contrast polepiece</pre>
 ===55-3. objective mini lens===
 The "objective mini lens" is a weakly excited lens placed below the objective lens. This lens does not have a polepiece to strengthen a magnetic field as the objective lens does. This lens is used to form an image on the selector aperture in Low MAG mode (～50× to 3,000×) by stopping the excitation of the objective lens. The magnification at the objective mini lens is 1× to 2×. This lens is also used to obtain a high quality low magnification image of about 1,000× in the MAG mode. That is, the excitation of the objective lens is kept strong to maintain image quality of the objective-lens, and the image is demagnified (to ～0.5×) by the objective mini lens, thus a wide view image is formed on the object plane of the intermediate lens.

←上一版本		2020年7月2日 (四) 03:13的版本
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	Compared with the C-TEM image, the ZPC-TEM image clearly visualizes the fine structures of DNA in a capsid, the hair-like structural objects and the cylindrical structures on the capsid surface.		Compared with the C-TEM image, the ZPC-TEM image clearly visualizes the fine structures of DNA in a capsid, the hair-like structural objects and the cylindrical structures on the capsid surface.
		+
		+	==96. Multi pole==
		+	The multi pole is an electron optical component for creating a symmetric magnetic field. It is used to correct the aberration of the objective lens.
		+	The multi pole is manufactured in such a way that, soft magnetic metal rods are coiled with copper wire and are placed radially and symmetrically with respect to the optical axis of the electron beam (Fig.(a)). According to a desired symmetry of magnetic field, various multi poles are designed. That is, a quadra-pole (Fig.(b)), a hexa-pole (Fig.(c)), an octa-pole (Fig.(d)) and a dodeca-pole (Fig.(e)) are used for TEM. The strength of the magnetic field on the optical axis is varied by adjusting the current applied to the coils.
		+	In the spherical aberration (Cs) corrector for the objective lens, a hexa-pole (Fig.(c)) or a dodeca-pole (Fig.(e)) is used to generate a three-fold symmetric magnetic field. There is also a Cs corrector composed of a quadra-pole (Fig.(b)) and an octa-pole (Fig.(d)).
		+	It is noted that, in the chromatic aberration (Cc) corrector for the objective lens, a multi pole where an electric field is superposed on a magnetic field is used.
		+
		+	[[文件:Multi pole 01.png]]
		+	a. Schematic of magnetic pole, coil, and magnetic field [B] in Quadra-pole
		+	b. Quadra-pole
		+	c. Hexa-pole
		+	d. Octa-pole
		+	e. Dodeca-pole

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 ==13. diffraction limit ==
 The diffraction limit is the resolution limit due to diffraction of an electron wave for the optical system with no aberrations. Even in the aberration-free optical system, electron waves exiting from one point on the object do not form an infinitesimal point on the image plane but these electron waves are focused into a finite size spot (airy disk) due to their diffraction phenomenon. The radius r of the airy disk is given by the equation r = 0.6λ/sinα, where λ is the wavelength of the electron and α is the divergence angle of the electron. From the equation, it is seen that the size of the airy disk is small for a large divergence angle of the electron beam. This limitation makes it impossible to produce an infinitesimal point resolution even for ideal lenses.
 [[文件:Diffraction limit-1.png]]