Texture details in experimental lattice images from a monolamellar paraffin crystal

1986 ◽  
Vol 44 ◽  
pp. 182-183
Author(s):  
D. L. Dorset ◽  
F. Zemlin ◽  
E. Reuber ◽  
E. Beckmann ◽  
E. Zeitler
Keyword(s):  
Crystal Structure ◽  
Electron Microscope ◽  
Phase Contrast ◽  
Objective Lens ◽  
Direct Visualization ◽  
Routine Procedure ◽  
Contrast Transfer Function ◽  
Lattice Images ◽  
Similar Images ◽  
Beam Damage

The direct visualization of crystal structure at "molecular" (ca 3Å) resolution has become a routine procedure in electron microscopy in the last few years for organic materials which are resistant to electron beam damage by virtue of π-electron derealization or electrical conductivity. More recently, similar images from an aliphatic material, i.e. the paraffin n-tetratetracontane, were published based on work with an electron microscope equipped with a He-cooled superconducting objective lens. Correlation-averaged electron images at 2.5A resolution were shown to correspond well to a theoretical image based on a multislice calculation for the known crystal structure and produced at the phase contrast transfer function of the electron microscope objective lens for the defocus value used in the experiment.

The information limit of a 200kv field emission TEM

1995 ◽  
Vol 53 ◽  
pp. 586-587
Author(s):  
T. Kaneyama ◽  
M. Kawasaki ◽  
T. Tomita ◽  
T. Honda ◽  
M. Kersker
Keyword(s):  
Thin Film ◽  
Electron Microscope ◽  
Field Emission ◽  
Phase Contrast ◽  
Mechanical Stability ◽  
Power Supplies ◽  
Objective Lens ◽  
Operating Parameters ◽  
Contrast Transfer Function ◽  
Transmission Electron

The Point resolution of a transmission electron microscope is normally defined by the reciprocal of the spatial frequency of the first zero in the phase contrast transfer function at the Scherzer defocus condition. When a field emission gun (FEG) is used as the electron source, the information limit, that point at which the contrast beyond the first zero goes to zero contrast, becomes equally important. We have investigated the primary microscope parameters that affect the information limit.A 200kV FE-TEM (JEM-2010F) equipped with a ZrO/W shottkey emitter and Gatan Parallel EELS (PEELS) was used for the experiments. The aberration coefficients of the objective lens are Cs = 1mm and Cc = 1.4mm. The specimen used is an evaporated amorphous Ge thin film with small gold islands.The resolution performance of the microscope depends not only on the performance of the objective lens, the high voltage stability, stability of the lens and deflector power supplies, operating parameters of the FEG, and the overall mechanical stability of the microscopes.

Practical Correction of Three Fold Astigmatism in the Philips CM TEM

1996 ◽  
Vol 54 ◽  
pp. 418-419
Author(s):  
Arno J. Bleeker ◽  
Mark H.F. Overwijk ◽  
Max T. Otten
Keyword(s):  
Optical Properties ◽  
Phase Contrast ◽  
The Other ◽  
Objective Lens ◽  
Symmetric Part ◽  
A Posteriori ◽  
Contrast Transfer Function ◽  
High Brightness ◽  
Rotationally Symmetric ◽  
Brightness Field

With the improvement of the optical properties of the modern TEM objective lenses the point resolution is pushed beyond 0.2 nm. The objective lens of the CM300 UltraTwin combines a Cs of 0. 65 mm with a Cc of 1.4 mm. At 300 kV this results in a point resolution of 0.17 nm. Together with a high-brightness field-emission gun with an energy spread of 0.8 eV the information limit is pushed down to 0.1 nm. The rotationally symmetric part of the phase contrast transfer function (pctf), whose first zero at Scherzer focus determines the point resolution, is mainly determined by the Cs and defocus. Apart from the rotationally symmetric part there is also the non-rotationally symmetric part of the pctf. Here the main contributors are not only two-fold astigmatism and beam tilt but also three-fold astigmatism. The two-fold astigmatism together with the beam tilt can be corrected in a straight-forward way using the coma-free alignment and the objective stigmator. However, this only works well when the coefficient of three-fold astigmatism is negligible compared to the other aberration coefficients. Unfortunately this is not generally the case with the modern high-resolution objective lenses. Measurements done at a CM300 SuperTwin FEG showed a three fold-astigmatism of 1100 nm which is consistent with measurements done by others. A three-fold astigmatism of 1000 nm already sinificantly influences the image at a spatial frequency corresponding to 0.2 nm which is even above the point resolution of the objective lens. In principle it is possible to correct for the three-fold astigmatism a posteriori when through-focus series are taken or when off-axis holography is employed. This is, however not possible for single images. The only possibility is then to correct for the three-fold astigmatism in the microscope by the addition of a hexapole corrector near the objective lens.

User Access to Lorentz Microscopy at the NCEM, LBNL, Berkeley.

1998 ◽  
Vol 4 (S2) ◽  
pp. 472-473
Author(s):  
K. Verbist ◽  
C. Nelson ◽  
K. Krishnan
Keyword(s):  
Electron Microscope ◽  
Phase Contrast ◽  
Limited Range ◽  
Objective Lens ◽  
Image Filter ◽  
Lorentz Microscopy ◽  
Differential Phase ◽  
Free Sample ◽  
User Access ◽  
Differential Phase Contrast

A standard Philips CM200FEG electron microscope, without the special Lorentz lens, has been optimized for Lorentz imaging. The necessary field-free sample region is obtained by switching off the objective lens in the free lens mode. The limited range of magnification is compensated for by a post-column Gatan image filter (GIF) which magnifies by a factor of _ 20. Fresnel imaging is performed by defocusing with the diffraction lens. The use of low angle diffraction, in combination with the apertures located at the selected area aperture plane, allow Foucault imaging. The TEM analog of differential phase contrast (DPC) imaging has been implemented. This method makes it possible to obtain quantitave induction maps of the in-plane magnetization. TEM DPC is based on a series of Foucault images, recorded with different incremental beam tilts, which are processed to yield images equivalent to the quadrant signals obtained by the STEM DPC technique.

Incoherent illumination method with conventional electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 174-175
Author(s):  
Fumio Nagata ◽  
Tsuyoshi Matsuda ◽  
Tsutomu Komoda ◽  
Kiyoshi Hama
Keyword(s):  
Electron Microscope ◽  
Contrast Effect ◽  
Phase Contrast ◽  
Carbon Film ◽  
Large Angle ◽  
Image Resolution ◽  
Experimental Investigations ◽  
Objective Lens ◽  
Glancing Angle ◽  
Strong Excitation

When fine details of thin films are observed, the image are generally composed of both amplitude and phase contrast. The image resolution is sometimes limited by the granular background noise of supporting film which is due to the phase contrast effect by fairly coherent illumination(CI).In the present work, incoherent illumination(ICI) method has been studied to avoid the phase contrast effect using a conventional electron microscope(Hitachi HU-12A).The ICI method was made by enlarging the illumination angle(β) to be equivalent to the glancing angle(α=1.4x10-2 radians) of objective aperture. The large angle illumination was achieved by the strong excitation of an objective lens.At first, the properties of phase contrast in ICI image were studied as functions of beam divergence angle and defocus using a carbon film. Both analytical and experimental investigations show that the granular noise in a phase contrast image decreases as β is increased from l×l0-4 to l×l0-2radians.

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.

Determination of the defocus value of micrographs of ice-embedded specimen without carbon support film

1993 ◽  
Vol 51 ◽  
pp. 560-561
Author(s):  
Z. Hong Zhou
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Transfer Function ◽  
Carbon Support ◽  
Objective Lens ◽  
Contrast Transfer Function ◽  
X Ray ◽  
Spatial Frequencies ◽  
High Resolution Reconstruction

It is well recognized that the contrast transfer function (CTF) of an electron microscope modulates the image contrast The effects of this CTF are to reverse the sign of the phases and to alter the amplitudes at different spatial frequencies. These changes are dependent on the defocus of the objective lens in a given microscope setting. Therefore, it is necessary to determine the defocus experimentally in order to correct the phase reversal and the amplitudes due to the CTF for attaining a high resolution reconstruction. The most straightforward way of determining the defocus value is to determine the positions of the Thon rings in the CTF by optical or computed transforms. In a crystalline specimen, the defocus value of an image can be refined against the electron diffraction amplitude. For specimen of which the x-ray structure is known, one can also use the x-ray structure factor to determine the CTF parameters.

Phase refinement of copper perchlorophthalocyanine from a 0.23 nm-resolution electron micrograph using the Sayre equation

1994 ◽  
Vol 52 ◽  
pp. 100-101
Author(s):  
Douglas L. Dorset ◽  
Sophie Kopp ◽  
John R. Fryer ◽  
William F. Tivol ◽  
James N. Turner
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Primary Source ◽  
Direct Methods ◽  
Ccd Camera ◽  
Basis Set ◽  
X Rays ◽  
Contrast Transfer Function ◽  
Lattice Images ◽  
Integrated Intensities

The use of direct methods of phasing for electron diffraction (ED) presents opportunities which cannot be matched with x-ray diffraction. High-resolution lattice images of thin crystals obtained on the electron microscope can provide crystallographic phases after image averaging and correction for the contrast transfer function--a procedure which has no analog for x-rays. This procedure has been used for protein crystallography, where such images are often the primary source for phase information.The method has also been used in the analysis of organic molecules.A high resolution (0.23 nm) electron microscope image of epitaxially oriented copper perchlorophthalocyanine obtained at 500 kV (Fig. 1) was used to provide a basis set of 39 phases for refinement in conjunction with a set of ED amplitudes obtained at 1200 kV (Fig 2). Portions of the image were digitized with a CCD camera and a frame-grabber and analyzed using the CRISP software package. The ED pattern was scanned using a Joyce-Loebl Mk. IIIC flatbed microdensitometer to produce integrated intensities, to which no Lorenz correction was applied.

Phase-contrast electron microscope lattice images of carbons

Carbon ◽  
1975 ◽  
Vol 13 (6) ◽  
pp. 547
Author(s):  
D Crawford ◽  
H Marsh
Keyword(s):  
Electron Microscope ◽  
Phase Contrast ◽  
Lattice Images

Phase Contrast Images of Periodic and Quasi-Periodic Objects

1967 ◽  
Vol 25 ◽  
pp. 234-235
Author(s):  
T. Komoda
Keyword(s):  
Contrast Effect ◽  
Phase Contrast ◽  
Periodic Structures ◽  
Present Report ◽  
Objective Lens ◽  
Electron Microscopic ◽  
Contrast Transfer Function ◽  
Electron Microscopic Image ◽  
Optical Transfer ◽  
Illuminating Beam

The phase contrast effect due to defocussing of an objective lens is decisive factor for imaging of molecular details in electron microscopy. The effect was intensively investigated by Thon) for amorphous objects. The present report is concerned with the phase contrast effect for the objects having periodic structures such as crystals and that of quasiperiodic ones.The contrast of the electron microscopic image has been theoretically treated by Hanszen) within the frame of the optical transfer theory. Phase contrast images are explained with a phase contrast transfer function, which shows the selective imaging of Fourier spectrum of spacial frequencies (reciprocal of periods) in the potential distribution in the object. The function diminishes under the conventional operating condition of the electron microscope. Fluctuation of focus and angular divergence of the illuminating beam are predominant factors for the diminishing.

Lattice Images of Non-Integer Planes in Gold

1971 ◽  
Vol 29 ◽  
pp. 182-183
Author(s):  
W. R. Bottoms ◽  
L. L. Ban
Keyword(s):  
Electron Diffraction ◽  
Phase Contrast ◽  
Objective Lens ◽  
Transmission Electron ◽  
Structure Factors ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
Lattice Planes ◽  
Gold Microcrystals

A common growth habit for gold microcrystals is a thin (111) platelet of hexagonal or trigonal symmetry. It has been shown that such microcrystals contain coherent faults in the ABCABC stacking sequence giving rise to non-zero structure factors for lattice planes of index 1/3(422). Transmission electron diffraction patterns from these crystals such as shown in Figure 2 confirm the existence of this non-zero structure factor by exhibiting reflections whose spacing and orientation correspond to lattice planes of the type 1/3(422). The diffraction pattern in Figure 2 has been superimposed on the polycrystalline ring pattern of gold for reference and the spacings of the inner-most spots is equal to the 2.497Å of the 1/3(422) planes to within the experimental error. Additional confirmation of the indexing of these spots has been obtained by electron diffraction at various angles of tilt.Phase contrast lattice images of the non-integer planes shown in Figure 1 were obtained with axial illumination of the sample by defocusing the objective lens of a Philips EM-300 electron microscope.

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