Displaced Aperture Dark Field Images by an Aberration Correction

1972 ◽  
Vol 30 ◽  
pp. 564-565
Author(s):  
K. Shirota ◽  
T. Yamamoto ◽  
T. Yanaka ◽  
O. Vingsbo
Keyword(s):  
Optical Axis ◽  
Dark Field Image ◽  
Image Plane ◽  
Dark Field ◽  
Objective Lens ◽  
Aberration Correction ◽  
Bright Field ◽  
Incident Electron Beam ◽  
Dark Field Microscopy ◽  
Electron Orbit

In displaced aperture dark field microscopy, the direction of the incident electron beam with respect to the specimen is maintained unaltered between bright field and dark field images, unlike the case of usual high resolution dark field microscopy by tilted illumination. The displaced aperture technique, however, gives a strong dark field image deterioration due to field aberrations. These are prounouncedly large since the deviation of the orbits of the imaging electrons from the optical axis is very large in this case. In the present paper, the improvement of the image quality by aberration correction is discussed.1. The chromatic field aberration is composed of components mainly from the objective and intermediate lenses. It can be corrected by changing the electron orbit by means of a beam deflector, introduced in the image plane of the objective lens.

Density-based discrimination of protein and RNA in the ribosome

1992 ◽  
Vol 50 (1) ◽  
pp. 464-465
Author(s):  
Joachim Frank
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Three Dimensional ◽  
Wiener Filter ◽  
Dark Field Image ◽  
Dark Field ◽  
Frequency Range ◽  
Bright Field ◽  
Contrast Transfer Function ◽  
Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

Dark Field Procedures in Electron Microscopy of Particulate Biological Material

1971 ◽  
Vol 29 ◽  
pp. 426-427
Author(s):  
E. de Harven ◽  
K. R. Leonard ◽  
A. K. Kleinschmidt
Keyword(s):  
Dark Field Image ◽  
Dark Field ◽  
Carbon Films ◽  
Objective Lens ◽  
Uranyl Ions ◽  
E Coli ◽  
Transmission Electron ◽  
Beam Stop ◽  
Electron Microscopes ◽  
Horse Spleen Ferritin

The dark field image of a specimen is obtained by allowing elastically scattered electrons to pass along the optic axis of the objective lens. Most of the inelastically scattered and the undeflected electrons are eliminated by various procedures, three of which have been found practical in conventional transmission electron microscopes. These three procedures are based on the use of: i) “beam stop” dark field apertures positioned in the back focal plane of the objective lens, as described by Thon; ii) electron beam tilted mechanically, or by a deflecting magnetic coil system between the condenser lens and the object; iii) a “cone mantle” illumination of the object obtained by an annular condenser aperture of appropriate dimension. Our observations have been made with Siemens Elmiskop 1A and 101 electron microscopes, equipped with pointed cathodes (single crystal or lancet-shaped). All samples were supported by ultrathin (2 to 3 nm) carbon films. They included: (a) various viral DNA-cytochrome c monolayers, (b) horse spleen ferritin, (c) B. Subtilis SP 50 bacteriophages, and (d) 50 S E. Coli ribosomal particles. Samples (c) and (d) were stained with uranyl ions.

Structures and defects identified by dark-field HREM

1992 ◽  
Vol 50 (1) ◽  
pp. 124-125
Author(s):  
J.P. Zhang
Keyword(s):  
High Resolution ◽  
Structural Information ◽  
Image Interpretation ◽  
Dark Field Image ◽  
Dark Field ◽  
Bright Field ◽  
Field Mode ◽  
Transmitted Beam ◽  
Structure Information ◽  
The Difference

The tilted illumination dark field high resolution imaging technique was applied to structures and defects of semiconductors and superconductors. We used a Hitachi-H9000 top entry microscope with a high resolution pole-piece of Cs=0.9 mm, operated at 300 Kv. Proper apertures, tilting angle and imaging conditions were chosen to minimize the phase shift due to aberrations. Since the transmitted beam was moved outside the aperture, the noise ratio was greatly reduced, which resulted in a significant enhancement of image contrast and apparent resolution. Images are not difficult to interpret if they have a clear correspondence to structure - information from image simulations in bright field mode can be used to assist in dark field image interpretation.An example in a semiconductor, GaAs/Ga0.49In0.51P2 superlattice imaged along [110] direction is shown in Figure 1. In this dark field image the GaAs and GaInP layers can be easily distinguished by their different contrast, and the difference in quality between both sides of interfaces is clear. An enlarged image in Figure 1 shows the defective area on the rough side of interface. Since this image shows the same pattern as the [110] projection of an fee structure, the major structural information about {111}, {200}, {220} planes can be obtained from this zone. Note that in bright field mode, [110] is not a good zone for imaging such multilayers.

scholarly journals PHOTOGRAPHIC CYTOPHOTOMETRY WITH A DUAL-MICROSCOPE. II. MICROSCOPE ASSEMBLY AND FILM-DYE EXTRACTIONS

1964 ◽  
Vol 12 (8) ◽  
pp. 600-607 ◽  
Author(s):  
JOHN W. KELLY ◽  
W. A. CLABAUGH ◽  
H. K. HAWKINS
Keyword(s):  
Fluorescence Polarization ◽  
Dry Mass ◽  
Dark Field ◽  
Bright Field ◽  
Spectrophotometric Measurement ◽  
Color Film ◽  
Microscopic Object ◽  
Dark Field Microscopy ◽  
Polarization Phase ◽  
Dye Solutions

Improved apparatus for dual-microscope photographic cytophotometry is described. The major component is a new comparison microscope, available commercially, whose binocular system is optically corrected for performance equivalent to that expected of one microscope. While current applications involve only standard bright-field and interference optics for absorption and dry-mass studies, a feature of the assembly is ready interchangeability of optics for fluorescence, polarization, phase, and dark-field microscopy. A method for extraction of color-film dyes into dimethylsulfoxide is reported. The dye solutions are used for spectrophotometric measurement of amount of dye in a given area of film and, indirectly, for estimating the amount of chromophore in the corresponding area of a microscopic object.

Experimental High Resolution Dark Field Electron Microscopy

1977 ◽  
Vol 35 ◽  
pp. 142-143
Author(s):  
Larry Pierce ◽  
Peter R. Buseck
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Dark Field ◽  
Objective Lens ◽  
Aperture Size ◽  
Bright Field ◽  
Chromatic Aberrations ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Diffraction Patterns

High resolution dark field (DF) images of the superstructures of the pyrrhotite (Fe1-xS) and bornite-digenite (Cu5FeS4-Cu9S5) series can be related to structure. Further, they provide more detail than bright field (BF) images. The same objective aperture size and stigmater settings were used for DF as for BF imaging; symmetrical arrangements of diffracted beams in the objective aperture were used. Images that can be related to structure were obtained at the defocus value giving the greatest image contrast, thereby enabling proper defocusing without requiring extensive through-focus series.For the minerals of interest, diffraction patterns consist of many superstructure reflections and a few subcell reflections. BF images contain primarily features of the superstructure, presumably because the subcell reflections fall far from the axis of the objective lens and thus are affected by spherical and chromatic aberrations and beam divergence. Likewise, DF images formed with a similar arrangement of beams as that in BF contain only features of superstructure, but with reverse contrast to BF.

Microdiffraction studies of small crystallites

1988 ◽  
Vol 46 ◽  
pp. 708-709
Author(s):  
S. A. Bradley ◽  
H. J. Robota
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Dark Field Image ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Angle Scattering ◽  
Dark Field Microscopy ◽  
Scanning Transmission ◽  
Annular Dark Field

Identification of nano-crystallites (<5 nm) on a high surface area support such as a catalyst is critical in the development of improved catalysts. Bright field imaging of small particles can be obscured by the phase contrast of the support. A common approach is to utilize annular dark field microscopy; however, wide angle scattering from the high surface area support can easily appear in the annular dark field image. Often one utilizes the energy dispersive detector to identify conclusively the nanosized metal crystallite, but this approach is troublesome when crystallites are very thin since counting times for imaging can become excessive. One technique for avoiding some of these difficulties is to utilize microdiffraction to identify the crystallite and then to image the crystallite by axial dark field microscopy.In the work reported here, the imaging was performed with a dedicated VG HB-5 scanning transmission electron microscope.

Dynamic Dark-Field Electron Microscopy

1976 ◽  
Vol 34 ◽  
pp. 482-483
Author(s):  
G.B. Haydon ◽  
R.A. Crane ◽  
C.R. Zercher
Keyword(s):  
Electron Microscopy ◽  
Optical Axis ◽  
Dark Field Image ◽  
Dark Field ◽  
Annular Ring ◽  
Field Electron ◽  
Field Electron Microscopy ◽  
Dark Field Electron

Dynamic dark-field electron microscopy as described here provides capabilities not present with other methods. An annular ring of any selected diameter is used to illuminate the specimen. Diffraction rings selected by the objective aperture are integrated photographically to produce the dark-field image.All methods of dark-field electron microscopy eliminate the incident illumination from the image and utilize only a selected portion of the scattered electrons and each has its limitations (1):1. Movement of the objective aperture off of the optical axis introduces spherical aberation which increases as the 4th power of the distance from the axis.2. Tilting the beam either mechanically or electrically allows only those electrons scattered in one direction to be imaged.

New imaging modes in STEM

1988 ◽  
Vol 46 ◽  
pp. 648-649
Author(s):  
A.V. Jones
Keyword(s):  
Energy Loss ◽  
Dark Field ◽  
Detector System ◽  
Objective Lens ◽  
Acceptance Angle ◽  
Bright Field ◽  
Dark Field Imaging ◽  
Annular Dark Field ◽  
Complex Forms ◽  
Field Imaging

The most often quoted advantage of STEM over conventional TEM is the ability to produce multiple simultaneous images by the use of multiple detector systems. In practice, this postulated advantage has seldom been fully utilised, mainly because of the practical difficulties in designing such detector systems.Most STEMs to date have been constructed as two-channel instruments combining annular dark-field imaging with either filtered bright-freld or inelastic imaging. More complex forms of bright-field detector have been employed1, as have parallel-readout systems for energy-loss spectra but the ability of the spectrometer to produce multiple simultaneous images has not been fully utilised.The basis of the problem lies in the fact that the objective lens and the detector system(s) have in most cases been designed by the manufacturers as separate entities in order to simplify the later addition of user-specific detectors. Since the acceptance angle of even the best spectrometers is relatively small, additional post-specimen lenses [with their attendant aberrations] had to be added in order to make full use of the spectrometer.

Dark-field electron spectroscopic imaging of aged microstructures in an aluminium lithium base alloy

1990 ◽  
Vol 48 (4) ◽  
pp. 444-445
Author(s):  
I. G. Solórzano ◽  
W. Probst
Keyword(s):  
Base Alloy ◽  
Spectroscopic Imaging ◽  
Chromatic Aberration ◽  
Dark Field ◽  
Objective Lens ◽  
Electron Spectroscopic Imaging ◽  
Bright Field ◽  
Field Mode ◽  
Dark Field Electron ◽  
Very High

The examination of microstructures make very high demands on the imaging quality and, therefore, on the instrumentation. In Al-Li base alloys it is of great interest to determine parameters such as size, distribution, morphology and coherency of precipitate phases as they dictate their mechanical behavior. In order to reveal morphological features with high quality the electron spectroscopic imaging (ESI) in dark field mode has shown to be quite a powerful technique.The ESI technique in the TEM is based on the possibility that accelerated electrons can be elastic and inelastically scattered by the sample atoms, as recently reviewed. The electron distribution in the transmitted and diffracted beams through a crystalline sample is such that both energy loss and elastic electrons will enter a typical objective aperture and thus contribute to both bright field and dark field images. The effect of the polyenergetic electrons is that the image is affected by chromatic aberration of the objective lens. In CTEM’s this effect is enhanced the lower the accelerating voltage and the thicker the sample.

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