Topic
Contrast transfer function
About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.
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Journal Article•
TL;DR: In this paper, a detailed discussion of the concept of resolutions in transmission electron microscopy and the effects of the optical aberrations is introduced, and the first results based on a 200kV TEM equipped with a Cs-corrector together with a monochromator are shown.
Abstract: Spherical aberration and chromatic aberrations are two fundamental optical imperfections that restrict the resolution of modern transmission electron microscopes (TEM). Nowadays,it reaches a limit that further development in lens design will inevitably conflict with the increasing demands of the large specimen space for some new applications,such as electron tomography,liquid-He cyro-microscopy and in-situ experiments. The invention of Cs-corrector may solve this dilemma,which greatly increases microscope point-resolution. The further improvement depends on the future Cc-corrector and,partially,the electron monochromator may do its job. After a detailed discussion of the concept of resolutions in transmission electron microscopy and the effects of the optical aberrations,the method of experimentally measuring resolution is introduced. Then the first results based on a 200kV TEM equipped with a Cs-corrector together with a monochromator are shown. Encouragingly,it confirms that the microscope resolution may reach a dimension below 0.1nm in a TEM with mediate voltage.
1 citations
TL;DR: In this article, the authors presented theory and simulations showing that this maximum spatial frequency can be increased considerably without loss of contrast by using a Zernike or Boersch phase plate that leads to a phase shift between scattered and unscattered electrons of only π /4, and recording images at Scherzer defocus.
Abstract: Summary
Zernike phase contrast has been recognized as a means of recording high-resolution images with high contrast using a transmission electron microscope. This imaging mode can be used to image typical phase objects such as unstained biological molecules or cryosections of biological tissue. According to the original proposal discussed in Danev and Nagayama (2001) and references therein, the Zernike phase plate applies a phase shift of π/2 to all scattered electron beams outside a given scattering angle and an image is recorded at Gaussian focus or slight underfocus (below Scherzer defocus). Alternatively, a phase shift of -π/2 is applied to the central beam using the Boersch phase plate. The resulting image will have an almost perfect contrast transfer function (close to 1) from a given lowest spatial frequency up to a maximum resolution determined by the wave length, the amount of defocus and the spherical aberration of the microscope. In this paper, I present theory and simulations showing that this maximum spatial frequency can be increased considerably without loss of contrast by using a Zernike or Boersch phase plate that leads to a phase shift between scattered and unscattered electrons of only π /4, and recording images at Scherzer defocus. The maximum resolution can be improved even more by imaging at extended Scherzer defocus, though at the cost of contrast loss at lower spatial frequencies.
Lay description
Zernike phase contrast has been recognized as a means of recording high-resolution images with high contrast using a transmission electron microscope. This imaging mode can be used to image specimens such as unstained biological molecules or sections of biological tissue. According to the original proposal, the Zernike phase plate applies a phase shift of π/2 to all scattered electron beams outside a given scattering angle and an image is recorded at or close to focus. The resulting image will be an almost perfect representation of the specimen up to a maximum resolution determined by the energy of the electrons and certain optical parameters of the microscope. In this paper, I present theory and simulations showing that this maximum resolution can be increased considerably without loss of contrast by using a Zernike phase plate that leads to a phase shift between scattered and unscattered electrons of only π/4, and recording images somewhat out of focus.
1 citations
Patent•
12 Jan 2012
TL;DR: In this article, the authors proposed a blocking member placed on the diffraction plane of a TEM, which blocks only electrons deflected at small angles, so that a contrast transfer function of the TEM according to the present invention is considered to be equal to that of a single-sideband microscope at low frequencies and a normal microscope at high frequencies.
Abstract: PROBLEM TO BE SOLVED: To provide a blocking member for use on a diffraction plane of a TEM.SOLUTION: The present invention relates to the blocking member placed on the diffraction plane of the TEM. The blocking member resembles a knife-edge used for imaging in a single sideband, but blocks only electrons deflected at small angles. Consequently, a contrast transfer function of the TEM according to the present invention is considered to be equal to that of a single-sideband microscope at low frequencies and that of a normal microscope at high frequencies. Preferable matter is that the highest frequency blocked by the blocking member is one at which a microscope having no blocking member is considered to show a CTF of 0.5.
1 citations
TL;DR: A domestic spherical aberration corrected 300 kV transmission electron microscope named R005, which stands for 0.05 nm resolution, was developed as mentioned in this paper, which has double aberration correctors in probe-forming and image-forming systems for high-resolution scanning transmission electron microscopy (STEM) and conventional TEM observation.
Abstract: A domestic spherical aberration corrected 300 kV transmission electron microscope named R005, which stands for 0.05 nm resolution, was developed. It has double aberration correctors in probe-forming and image-forming systems for high-resolution scanning transmission electron microscope (STEM) and conventional transmission electron microscope (TEM) observation. Asymmetric corrector optic system was developed to compress the parasitic aberration and the increase of chromatic aberration. Automatic aberration correction systems for STEM and TEM have been implemented. Neighboring atomic columns of Ga (63 pm spacing) in a GaN [211] crystalline specimen was resolved in a high angle annular dark field (HAADF) STEM image for the first time.
1 citations
TL;DR: High-resolution electron microscopy was used to detect the surface Fe3O4 iron-oxide layer formed on Fe4N iron nitride due to electron irradiation in the transmission electron microscope, and the existence of a surface oxide layer was confirmed by both image processing and through-focus observation.
Abstract: High-resolution electron microscopy (HREM) was used to detect the surface Fe 3 O 4 iron-oxide layer formed on [011] Fe 4 N iron nitride due to electron irradiation in the transmission electron microscope. The existence of asurface oxide layer was confirmed by both image processing and through-focus observation. Images of the iron oxide were revealed using the process of fast Fourier transformation (FFT) of experimental HREM images, filtering of the FFT patterns and inverse FFT. By through-focus observation, HREM images of iron oxide were obtained based on the tuning of contrast transfer function. Fourier filtering is effective for examining the beginning of phase transformation, because at this stage the diffraction spots of iron oxide are too weak to be detected. At the time when the iron oxide layer has developed to some extent, through-focus observation is useful to obtain an image of oxide layers.
1 citations