STEM Electron Diffraction and High-Resolution Images Used in the Determination of the Crystal Structure of the Au144(SR)60 Cluster

For well over two decades computers have played an important role in electron microscopy; they now pervade the whole field - as indeed they do in so many other aspects of our lives. The initial use of computers was mainly for large (as it seemed then) off-line calculations for image simulations; for example, of dislocation images.Image simulation has continued to be one of the most notable uses of computers particularly since it is essential to the correct interpretation of high resolution images. In microanalysis, too, the computer has had a rather high profile. In this case because it has been a necessary part of the equipment delivered by manufacturers. By contrast the use of computers for electron diffraction analysis has been slow to prominence. This is not to say that there has been no activity, quite the contrary; however it has not had such a great impact on the field.

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High-Resolution Image Simulation of a Tilted Crystal

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179099 ◽

1990 ◽

Vol 48 (1) ◽

pp. 68-69

Author(s):

C. J. D. Hetherington

Keyword(s):

High Resolution ◽

Crystal Thickness ◽

Thin Specimen ◽

Atomic Structures ◽

Kikuchi Lines ◽

High Resolution Images ◽

Final Estimate ◽

Simulated Images ◽

Habit Planes

Most high resolution images are not directly interpretable but must be compared with simulations based on model atomic structures and appropriate imaging conditions. Typically, the only parameters that are adjusted, in addition to the structure models, are crystal thickness and microscope defocus. Small tilts of the crystal away from the exact zone axis have only rarely been considered. It is shown here that, in the analysis of an image of a silicon twin intersection, the crystal tilt could be accurately estimated and satisfactorily included in the simulations.The micrograph shown in figure 1 was taken as part of an HREM study of indentation-induced hexagonal silicon. In this instance, the intersection of two twins on different habit planes has driven the silicon into hexagonal stacking. However, in order to confirm this observation, and in order to investigate other defects in the region, it has been necessary to simulate the image taking into account the very apparent crystal tilt. The inability to orientate the specimen at the exact [110] zone was influenced by i) the buckling of the specimen caused by strains at twin intersections, ii) the absence of Kikuchi lines or a clearly visible Laue circle in the diffraction pattern of the thin specimen and iii) the avoidance of radiation damage (which had marked effects on images taken a few minutes later following attempts to realign the crystal.) The direction of the crystal tilt was estimated by observing which of the {111} planes remained close to edge-on to the beam and hence strongly imaged. Further refinement of the direction and magnitude of the tilt was done by comparing simulated images to experimental images in a through-focal series. The presence of three different orientations of the silicon lattice aided the unambiguous determination of the tilt. The final estimate of a 0.8° tilt in the 200Å thick specimen gives atomic columns a projected width of about 3Å.

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A Simple Real-Space Channelling Theory for Electron Diffraction and HREM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179075 ◽

1990 ◽

Vol 48 (1) ◽

pp. 64-65

Author(s):

D. Van Dyck

Keyword(s):

High Resolution ◽

Electron Diffraction ◽

Direct Method ◽

Real Space ◽

Zone Axis ◽

Phase Object ◽

High Resolution Images ◽

The Many ◽

Analytical Expressions ◽

Electron Wavefunction

The computation of the many beam dynamical electron diffraction amplitudes or high resolution images can only be done numerically by using rather sophisticated computer programs so that the physical insight in the diffraction progress is often lost. Furthermore, it is not likely that in this way the inverse problem can be solved exactly, i.e. to reconstruct the structure of the object from the knowledge of the wavefunction at its exit face, as is needed for a direct method [1]. For this purpose, analytical expressions for the electron wavefunction in real or reciprocal space are much more useful. However, the analytical expressions available at present are relatively poor approximations of the dynamical scattering which are only valid either for thin objects ((weak) phase object approximation, thick phase object approximation, kinematical theory) or when the number of beams is very limited (2 or 3). Both requirements are usually invalid for HREM of crystals. There is a need for an analytical expression of the dynamical electron wavefunction which applies for many beam diffraction in thicker crystals. It is well known that, when a crystal is viewed along a zone axis, i.e. parallel to the atom columns, the high resolution images often show a one-to-one correspondence with the configuration of columns provided the distance between the columns is large enough and the resolution of the instrument is sufficient. This is for instance the case in ordered alloys with a column structure [2,3]. From this, it can be suggested that, for a crystal viewed along a zone axis with sufficient separation between the columns, the wave function at the exit face does mainly depend on the projected structure, i.e. on the type of atom columns. Hence, the classical picture of electrons traversing the crystal as plane-like waves in the directions of the Bragg beams which historically stems from the X-ray diffraction picture, is in fact misleading.

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Combined Experimentaland Theoretical Determination of the Atomic Structure of the (310) Twin in NB

MRS Proceedings ◽

10.1557/proc-238-163 ◽

1991 ◽

Vol 238 ◽

Cited By ~ 3

Author(s):

Geoffrey H. Campbells ◽

Wayne E. King ◽

Stephen M. Foiles ◽

Peter Gumbsch ◽

Manfred Rühle

Keyword(s):

High Resolution ◽

Theoretical Models ◽

High Resolution Electron Microscopy ◽

Interatomic Potentials ◽

Image Simulation ◽

Theoretical Determination ◽

Atomic Structures ◽

Resolution Electron ◽

High Resolution Images

ABSTRACTA (310) twin boundary in Nb has been fabricated by diffusion bonding oriented single crystals and characterized using high resolution electron microscopy. Atomic structures for the boundary have been predicted using different interatomic potentials. Comparison of the theoretical models to the high resolution images has been performed through image simulation. On the basis of this comparison, one of the low energy structures predicted by theory can be ruled out.

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3P-094 High resolution and precise X-ray crystal structure determination of Cyctochrome c Oxidase(The 46th Annual Meeting of the Biophysical Society of Japan)

Seibutsu Butsuri ◽

10.2142/biophys.48.s142_1 ◽

2008 ◽

Vol 48 (supplement) ◽

pp. S142

Author(s):

Michihiro Suga ◽

Kyoko Ito-Shinzawa ◽

Hiroshi Aoyama ◽

Kazumasa Muramoto ◽

Eiki Yamashita ◽

...

Keyword(s):

Crystal Structure ◽

High Resolution ◽

Annual Meeting ◽

Structure Determination ◽

Crystal Structure Determination ◽

X Ray ◽

Biophysical Society

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The crystal structure determination of dimethylsulphide by high-resolution neutron powder diffraction

Journal of Molecular Structure ◽

10.1016/s0022-2860(97)00102-6 ◽

1997 ◽

Vol 415 (3) ◽

pp. 259-266 ◽

Cited By ~ 5

Author(s):

R.M. Ibberson ◽

P.J. McDonald ◽

M. Pinter-Krainer

Keyword(s):

Crystal Structure ◽

High Resolution ◽

Powder Diffraction ◽

Structure Determination ◽

Neutron Powder Diffraction ◽

Crystal Structure Determination

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Atomic structure of YB56 studied by digital high-resolution electron microscopy and electron diffraction

Journal of Materials Research ◽

10.1557/jmr.2001.0019 ◽

2001 ◽

Vol 16 (1) ◽

pp. 101-107 ◽

Cited By ~ 6

Author(s):

Takeo Oku ◽

Jan-Olov Bovin ◽

Iwami Higashi ◽

Takaho Tanaka ◽

Yoshio Ishizawa

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Electron Diffraction ◽

High Resolution Electron Microscopy ◽

Charge Coupled Device ◽

X Ray ◽

Resolution Electron ◽

High Resolution Images ◽

Diffraction Patterns ◽

Simulated Images

Atomic positions for Y atoms were determined by using high-resolution electron microscopy and electron diffraction. A slow-scan charge-coupled device camera which had high linearity and electron sensitivity was used to record high-resolution images and electron diffraction patterns digitally. Crystallographic image processing was applied for image analysis, which provided more accurate, averaged Y atom positions. In addition, atomic disordering positions in YB56 were detected from the differential images between observed and simulated images based on x-ray data, which were B24 clusters around the Y-holes. The present work indicates that the structure analysis combined with digital high-resolution electron microscopy, electron diffraction, and differential images is useful for the evaluation of atomic positions and disordering in the boron-based crystals.

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