Electron Microscope Image Contrast for Thin Crystal

1972 ◽  
Vol 27 (3) ◽  
pp. 445-451 ◽  
Author(s):  
J. M. Cowley ◽  
Sumio Iijima
Keyword(s):  
Electron Microscope ◽  
Phase Contrast ◽  
Complex Oxide ◽  
Phase Shifts ◽  
Image Contrast ◽  
Crystal Thickness ◽  
Contrast Imaging ◽  
Resolution Electron ◽  
Unit Cells ◽  
Correct Account

AbstractHigh resolution electron microscope images showing the detailed distribution of metal atoms within the unit cells of complex oxide structures have been recorded recently and as a first approximation may be interpreted as amplitude-object images if obtained with the degree of defocus corresponding to the "optimum-defocus condition" for the phase-contrast imaging of thin phase objects. Detailed observations of images of Ti2Nb10O29 crystals having thicknesses of the order of 100 Å reveal that the thin phase-object approximation, which assumes that only small phase-shifts are involved, is inadequate to explain some features of the image intensities including the variation of contrast with crystal thickness. A very aproximate treatment of the phase contrast due to defocussing of phase objects having large phase shifts is evolved and shown to give a qualitativity correct account of the observations. The variation of image contrast with tilt away from a principle orientation is discussed. From the symmetry of the image contrast it is deduced that the symmetry of the crystal structure as derived from X-ray diffraction studies can not be correct.

Quantitative Electron Microscope with imaging plate

1994 ◽  
Vol 52 ◽  
pp. 408-409
Author(s):  
D. Shindo
Keyword(s):  
Electron Microscope ◽  
Dynamic Range ◽  
Processing System ◽  
Digital Data ◽  
Imaging Plate ◽  
Crystal Thickness ◽  
X Ray Diffraction ◽  
Resolution Electron ◽  
Electron Intensity ◽  
Diffraction Patterns

Imaging plate has good properties, i.e., a wide dynamic range and good linearity for the electron intensity. Thus the digital data (2048x1536 pixels, 4096 gray levels in log scale) obtained with the imaging plate can be used for quantification in electron microscopy. By using the image processing system (PIXsysTEM) combined with a main frame (ACOS3900), quantitative analysis of electron diffraction patterns and high-resolution electron microscope (HREM) images has been successfully carried out.In the analysis of HREM images observed with the imaging plate, quantitative comparison between observed intensity and calculated intensity can be carried out by taking into account the experimental parameters such as crystal thickness and defocus value. An example of HREM images of quenched Tl2Ba2Cu1Oy (Tc = 70K) observed with the imaging plate is shown in Figs. 1(b) - (d) comparing with a structure model proposed by x-ray diffraction study of Fig. 1 (a). The image was observed with a JEM-4000EX electron microscope (Cs =1.0 mm).

Fabrication of a Boersch phase plate for phase contrast imaging in a transmission electron microscope

2006 ◽  
Vol 77 (3) ◽  
pp. 033701 ◽  
Author(s):  
K. Schultheiß ◽  
F. Pérez-Willard ◽  
B. Barton ◽  
D. Gerthsen ◽  
R. R. Schröder
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Phase Contrast ◽  
Phase Contrast Imaging ◽  
Phase Plate ◽  
Contrast Imaging ◽  
Transmission Electron

Extension of the “thin-crystal” condition by small crystal tilts: Why HREM images of SiC polytypes always look tilted

1992 ◽  
Vol 50 (1) ◽  
pp. 116-117
Author(s):  
Michael A. O'Keefe ◽  
Velimir Radmilovic
Keyword(s):  
Silicon Carbide ◽  
Electron Microscope ◽  
High Resolution ◽  
Group Symmetry ◽  
Crystal Thickness ◽  
Resolution Electron ◽  
Microscope Images ◽  
High Resolution Electron Microscope ◽  
Simulated Images ◽  
Thin Crystal

Both experimental and simulated high-resolution electron microscope images of silicon carbide polytypes commonly exhibit symmetry changes in thicker crystal regions compared to the perfect (projected) space group symmetry of images from thin crystals. However, the changes predicted by simulation, and those found experimentally, are quite different.High-resolution transmission electron microscope images of silicon carbide polytypes were obtained with the JEOL ARM-1000 high-resolution electron microscope in the course of an investigation into a series of metal matrix composites. Like all HRTEM images of silicon carbide, these images failed to show the correct symmetry in the thicker parts of the specimen. Changes in image symmetry as crystal thickness is increased also occur when images of silicon carbide are simulated; for example, Smith and O'Keefe simulated images of polytypes of silicon carbide for crystals oriented so that the electron beam was precisely along the <1210> direction, and found marked departure from thin-crystal symmetry at thicknesses of the order of 150Å for an electron energy of 500keV. However, the lack of symmetry in their simulated images appears to be due to the presence of many second-order terms contributing to the intensity spectra of the thick-crystal images, whereas the symmetry changes in experimental images from thicker crystals are usually of the form that preserves the thin-crystal-like contrast for one set of “twin” spots, yet smears out the contrast of the other. A typical example of this latter effect can be seen in the image of the 6H variant of SiC shown in figure 1.

Computer Simulation of Electron Microscope Images from Atomic Structure Models

1985 ◽  
Vol 63 ◽  
Author(s):  
William Krakow
Keyword(s):  
Computer Simulation ◽  
Electron Microscope ◽  
High Resolution ◽  
Atomic Structure ◽  
Boundary Structure ◽  
Contrast Imaging ◽  
Large Atom ◽  
Resolution Electron ◽  
Microscope Images ◽  
Digital Frame

ABSTRACTIt is generally the case that simple direct interpretation of high resolution electron microscope images is not possible due to the phase contrast imaging modes necessary to achieve atomic level spatial resolution. Therefore, an extensive number of computer programs have been developed to perform electron diffraction and image computations. Both single scattering or dynamical scattering processes can be simulated as well as any form of imaging mode currently available on most modern high performance transmission electron microscopes. Since one is interested in imperfections rather than perfect crystal structures, a large number of sampling points in real and reciprocal space are required. Often, large atom position arrays must be sampled requiring large mainframe computer memories and fast CPU's. High quality displays are also required for realistic image representations and even faster computational methods via television rate digital frame store devices. This paper will be centered about a number of materials areas requiring high resolution electron microscopy computer simulation from atomic structure models. These areas include: organometallic molecules, point defects, surface structure and reconstructions, amorphous thin films, quasi-crystals, semiconductor interfaces and grain boundary structure in metals.

scholarly journals Advancing conventional High-Resolution Electron Microscopy

1991 ◽  
Vol 49 ◽  
pp. 652-653
Author(s):  
Ronald Gronsky
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Phase Contrast ◽  
High Resolution Electron Microscopy ◽  
Phase Contrast Imaging ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Imaging Resolution ◽  
Electron Microscopes

Due to the exceptional performance of most modern commercial transmission electron microscopes, the achievement of phase-contrast imaging resolution in the sub-2Å range is today a routine exercise, provided the samples are compliant. Nonetheless, there remains room for improvement, and the purpose of this manuscript is to highlight procedures that might be employed by the practicing microscopist for advancing conventional high resolution electron microscopy.

scholarly journals X-ray phase-contrast imaging with engineered porous materials over 50 keV

2018 ◽  
Vol 25 (4) ◽  
pp. 1182-1188 ◽  
Author(s):  
Hongchang Wang ◽  
Biao Cai ◽  
Matthew James Pankhurst ◽  
Tunhe Zhou ◽  
Yogesh Kashyap ◽  
...  
Keyword(s):  
Porous Materials ◽  
Phase Contrast ◽  
High Energy ◽  
Image Contrast ◽  
Alternative Solution ◽  
Phase Contrast Imaging ◽  
Contrast Imaging ◽  
Major Barrier ◽  
X Ray ◽  
Wide Range

X-ray phase-contrast imaging can substantially enhance image contrast for weakly absorbing samples. The fabrication of dedicated optics remains a major barrier, especially in high-energy regions (i.e. over 50 keV). Here, the authors perform X-ray phase-contrast imaging by using engineered porous materials as random absorption masks, which provides an alternative solution to extend X-ray phase-contrast imaging into previously challenging higher energy regions. The authors have measured various samples to demonstrate the feasibility of the proposed engineering materials. This technique could potentially be useful for studying samples across a wide range of applications and disciplines.

Effect of the Substrate on Image Contrast in High Resolution

1967 ◽  
Vol 25 ◽  
pp. 232-233 ◽  
Author(s):  
Claire B. Eisenhandler ◽  
Benjamin M. Siegel
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Phase Contrast ◽  
Biological Molecules ◽  
Structural Detail ◽  
Cornell University ◽  
Resolution Electron ◽  
Computer Calculations ◽  
High Resolution Electron Microscope ◽  
Molecular Images

A high resolution electron microscope intended for the study of thin biological molecules is currently under development at Cornell University. Previously reported computer calculations of the molecular images to be expected from this instrument indicate that considerable atomic structural detail would be visible in the image, specifically that atoms having Z≥6 would exhibit sufficient phase contrast to be observed and interatomic spacings ≳2Åwould be resolved. These earlier calculations did not consider the effect on the image of the substrate supporting the specimen. Results of a theoretical investigation of the substrate and computer calculations are presented here.

Crystal Structures Of L-Nb205 AND L-Ta205

1977 ◽  
Vol 35 ◽  
pp. 188-189
Author(s):  
Sumio Iijima
Keyword(s):  
Electron Microscope ◽  
Complex Nature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Resolution Electron ◽  
Unit Cells ◽  
System 2 ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns ◽  
Phase Relationships

Although structures of tantalum pentoxides have been extensively studied, they have not been fully understood because of the complex nature of their X-ray diffraction patterns. In this study we made some observations on crystals of L-Ta2O5 and L-Nb2O5 using a high resolution electron microscope. The latter structure has been believed to be isostructural with L-Ta2O5. The samples were prepared by Dr. Roth at NBS and were parts of the products used for determining phase relationships in niobium pentoxides (1) and the Ta2O5-Ta2WO8 system (2).According to the X-ray data both structures have orthorhombic unit cells with a = 6.2, b = 29.3, c = 3.9Å. The structures are based on the U03-type and the b spacings are nearly 8 times those of the subcell. Electron diffraction (E.D.) patterns of L-Nb2O5 and L-Ta3O5 crystals showing a*-b* reciprocal sections confirmed generally the results of X-ray works (Figs, la and lc).

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