Practical aspects about hollow-cone imaging

1995 ◽  
Vol 53 ◽  
pp. 576-577
Author(s):  
T. Geipel ◽  
W. Mader
Keyword(s):  
Electron Microscope ◽  
Transfer Function ◽  
Phase Contrast ◽  
Hollow Cone ◽  
Low Resolution ◽  
Contrast Transfer Function ◽  
Imaging Parameters ◽  
Specimen Holder ◽  
Optimum Imaging

Hollow-cone imaging (HCI) as a possibility to improve the resolution of a TEM has already been proposed in the late 40ties and besides others, there have been extensive hollow-cone experiments 10 years back using a low resolution TEM with a non-tilt specimen holder. In a recent paper the optimum imaging parameters for HCI were determined leading to an improvement of the resolution by a factor of two. However, there are contrast limitations and experimental problems for HCI which were only partly considered in Ref. and which will be discussed in this paper for a modern electron microscope. Preliminary experiments were performed which are not shown in the abstract.In Fig. 1 ∫ ct f(u)du is plotted versus defocus Δ f for different cone radii Θc and a fixed aperture radius Θo = 1/δ = 5 nm-1 (ct f is the phase contrast transfer function (PCTF) for HCI and δ = 0.2 nm is the resolution of a CM30 supertwin microscope).

Cryoelectron microscopy and image reconstruction of spherical viruses with spot scan and FEG technologies

1995 ◽  
Vol 53 ◽  
pp. 1086-1087
Author(s):  
N. H. Olson ◽  
U. Lücken ◽  
S. B. Walker ◽  
M. T. Otten ◽  
T. S. Baker
Keyword(s):  
Electron Microscope ◽  
Transfer Function ◽  
Field Emission ◽  
Phase Contrast ◽  
Atomic Resolution ◽  
Bright Spot ◽  
Biological Macromolecules ◽  
Contrast Transfer Function ◽  
Transmission Electron ◽  
Chlorotic Mottle

The field emission gun electron microscope (FEG) is a tool that has the potential to achieve near atomic resolution information of biological macromolecules. The FEG provides a beam with higher spatial and temporal coherence and a better phase contrast transfer function than do microscopes with either tungsten or LaB6 filaments. The FEG is also ideal for spot scan imaging applications because it can produce a small, coherent and very bright spot. In spot scan mode the specimen is exposed to an array of nonoverlapping spots rather man a flood beam. This significantly reduces beam-induced specimen drift.Frozen-hydrated samples of cowpea chlorotic mottle (CCMV, Fig. 1A) and cowpea severe mosaic virus (CPSMV, Fig. IB) were examined on a Philips CM12 transmission electron microscope equipped with a standard LaB6 gun and on a Philips CM200 equipped with a field emission gun, respectively. The CM12 was operated at 120kV and was externally controlled by means of a spot scan imaging program which produced a series of 250 nm diameter spots on Kodak SO-163 sheet film.

Radiation Damage of Support Films

1981 ◽  
Vol 39 ◽  
pp. 28-29
Author(s):  
H.A. Cohen ◽  
W. Chiu
Keyword(s):  
Transfer Function ◽  
Low Temperatures ◽  
Carbon Support ◽  
Contrast Transfer Function ◽  
Electron Dose ◽  
Imaging Parameters ◽  
Negative Stain ◽  
Phase Corrections ◽  
Two Parameters ◽  
Medium Dose

The goal of imaging the finest detail possible in biological specimens leads to contradictory requirements for the choice of an electron dose. The dose should be as low as possible to minimize object damage, yet as high as possible to optimize image statistics. For specimens that are protected by low temperatures or for which the low resolution associated with negative stain is acceptable, the first condition may be partially relaxed, allowing the use of (for example) 6 to 10 e/Å2. However, this medium dose is marginal for obtaining the contrast transfer function (CTF) of the microscope, which is necessary to allow phase corrections to the image. We have explored two parameters that affect the CTF under medium dose conditions.Figure 1 displays the CTF for carbon (C, row 1) and triafol plus carbon (T+C, row 2). For any column, the images to which the CTF correspond were from a carbon covered hole (C) and the adjacent triafol plus carbon support film (T+C), both recorded on the same micrograph; therefore the imaging parameters of defocus, illumination angle, and electron statistics were identical.

Evaluation method for imaging plate resolution by means of phase contrast transfer function

1995 ◽  
Vol 53 ◽  
pp. 662-663 ◽  
Author(s):  
T. Oikawa ◽  
H. Kosugi ◽  
F. Hosokawa ◽  
D. Shindo ◽  
M. Kersker
Keyword(s):  
Transfer Function ◽  
Phase Contrast ◽  
Evaluation Method ◽  
Amorphous Film ◽  
Imaging Plate ◽  
X Rays ◽  
Special Shape ◽  
Contrast Transfer Function ◽  
Contrast Image ◽  
Specimen Shape

Evaluation of the resolution of the Imaging Plate (IP) has been attempted by some methods. An evaluation method for IP resolution, which is not influenced by hard X-rays at higher accelerating voltages, was proposed previously by the present authors. This method, however, requires truoblesome experimental preperations partly because specially synthesized hematite was used as a specimen, and partly because a special shape of the specimen was used as a standard image. In this paper, a convenient evaluation method which is not infuenced by the specimen shape and image direction, is newly proposed. In this method, phase contrast images of thin amorphous film are used.Several diffraction rings are obtained by the Fourier transformation of a phase contrast image of thin amorphous film, taken at a large under focus. The rings show the spatial-frequency spectrum corresponding to the phase contrast transfer function (PCTF). The envelope function is obtained by connecting the peak intensities of the rings. The evelope function is offten used for evaluation of the instrument, because the function shows the performance of the electron microscope (EM).

Correction of the contrast transfer function to determine the radial density distribution of frozen-hydrated tobacco mosaic virus

1992 ◽  
Vol 50 (1) ◽  
pp. 536-537
Author(s):  
Michael F. Smith ◽  
John P. Langmore
Keyword(s):  
Transfer Function ◽  
Phase Contrast ◽  
Heavy Atom ◽  
Biological Molecules ◽  
Frequency Compensation ◽  
Contrast Transfer Function ◽  
High Background ◽  
Low Contrast ◽  
Radial Density Distribution ◽  
Excellent Preservation

The purpose of image reconstruction is to determine the mass densities within molecules by analysis of the intensities within images. Cryo-EM offers this possibility by virtue of the excellent preservation of internal structure without heavy atom staining. Cryo-EM images, however, have low contrast because of the similarity between the density of biological material and the density of vitreous ice. The images also contain a high background of inelastic scattering. To overcome the low signal and high background, cryo-images are typically recorded 1-3 μm underfocus to maximize phase contrast. Under those conditions the image intensities bear little resemblance to the object, due to the dependence of the contrast transfer function (CTF) upon spatial frequency. Compensation (i.e., correction) for the CTF is theoretically possible, but implementation has been rare. Despite numerous studies of molecules in ice, there has never been a quantitative evaluation of compensated images of biological molecules of known structure.

High Resolution TEM Imaging with Hollow-Cone Illumination

1997 ◽  
Vol 3 (S2) ◽  
pp. 1191-1192 ◽  
Author(s):  
Maxim V. Sidorov ◽  
Martha R. McCartney ◽  
David J. Smith
Keyword(s):  
High Resolution ◽  
Transfer Function ◽  
Phase Contrast ◽  
Resolution Enhancement ◽  
Expected Improvement ◽  
Practical Application ◽  
Hollow Cone ◽  
High Resolution Tem

It has long been realized that imaging with hollow cone illumination (HCI) should, in theory, improve the directly interpretable resolution of TEM by as much as 100% (albeit at the expense of contrast). The principle of HCI was first proposed by Scherzer in 1949 and then reinvented by Hanssen and Trepte in 1971. As opposed to axial illumination, HCI effectively eliminates zeroes and reversals of the transfer function providing direct interpretability of the resulting images. In addition to the substantial resolution enhancement, HCI should reduce significantly the phase-contrast noise inherent in axial HRTEM images. However, there are experimental obstacles for high resolution HCI which make its practical application very difficult to implement. To our knowledge, all observations using HCI so far have not shown all of the expected improvement predicted theoretically. This is believed to be due to the fact that accurate coma-free alignment is required to substantially improve the resolution.

Sideband imaging for sub-Å image resolution with an intermediate voltage conventional TEM

1991 ◽  
Vol 49 ◽  
pp. 412-413
Author(s):  
William Krakow
Keyword(s):  
Electron Microscope ◽  
Transfer Function ◽  
Amorphous Materials ◽  
Image Features ◽  
Image Resolution ◽  
Objective Lens ◽  
Contrast Transfer Function ◽  
Image Artifact ◽  
Cornell University ◽  
The Many

The impetus for achieving sub-angstrom resolution in a CTEM was put in place several years ago at Cornell University in the laboratory of Professor Benjamin Siegel. Amongst the many activities in his laboratory was the mission to retrieve and restore the information contained in HREM images by correcting the deleterious effects of the objective lens contrast transfer function. At this time, micrographs of amorphous materials such as Ge were being studied elsewhere with the premise that tilting the illumination would lead to improved resolution. This in fact led to the observation of fringe-like image features which could not be explained in terms of an amorphous material's microstructure. At this time we were able to demonstrate in Professor Siegel's laboratory that the appearance of pseudo fringe structures was an image artifact produced by spatial filtering in the electron microscope of elastically and inelastically scattered electrons.

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