Effect of diffraction crystallography on HREM

2003 ◽  
Vol 218 (4) ◽  
Author(s):  
Fang-hua Li
Keyword(s):  
Image Processing ◽  
High Resolution ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Heavy Atom ◽  
Empirical Method ◽  
Crystal Defects ◽  
Electron Diffraction Data ◽  
Crystal Thickness ◽  
Resolution Electron

AbstractA simple image contrast theory in high-resolution electron microscopy (HREM) is introduced to demonstrate that below a certain critical crystal thickness the intensity of the Scherzer focus image is linear to the projected potential of an artificial crystal that is isomorphic to the examined one. It has become the theoretical base of electron crystallographic image processing techniques relying on the weak-phase-object approximation and kinematical diffraction. Two techniques of image processing are introduced. One of them aims at determining crystal structures by combining electron diffraction data and applying diffraction analysis methods. To reduce various kinds of electron diffraction intensity distortion the diffraction data are corrected by means of an empirical method set up by referring to the heavy atom method and Wilson statistic. The other one aims at revealing crystal defects at atomic resolution from the image taken with a medium-voltage field-emission high-resolution electron microscope. The dynamical effect is corrected by forcing the integral amplitudes of reflections in the diffractogram of image equal to the amplitudes of corresponding structure factors for the perfect crystal. The principle of the two techniques is briefly introduced, and examples of applications to crystal structure and defect determination are given.

Electron Crystallography of Phthalocyanines

1999 ◽  
Vol 03 (07) ◽  
pp. 672-678 ◽  
Author(s):  
J. R. FRYER
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Structural Information ◽  
High Resolution Electron Microscopy ◽  
Electron Diffraction Data ◽  
Electron Crystallography ◽  
Resolution Electron ◽  
Copper Phthalocyanines

It is shown that it is possible to obtain structural information from small (<100 nm) phthalocyanine crystals by using crystallographic direct phasing methods applied to electron diffraction data. This technique is both quantitative and does not suffer from the difficulties associated with high-resolution electron microscopy. Structural information has been obtained from both tetra- and octa chloro-copper phthalocyanines, and the results compared with the hydrogenated and perchloro members of the series.

STRUCTURE DETERMINATION OF THE Ge(111)-(3×1)Ag SURFACE RECONSTRUCTION

1999 ◽  
Vol 06 (06) ◽  
pp. 1061-1065 ◽  
Author(s):  
D. GROZEA ◽  
E. BENGU ◽  
C. COLLAZO-DAVILA ◽  
L. D. MARKS
Keyword(s):  
Electron Diffraction ◽  
Surface Reconstruction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Heavy Atom ◽  
Direct Methods ◽  
Electron Diffraction Data ◽  
Transmission Electron ◽  
First Time

For the first time, during the investigation of the Ag submonolayer on the Ge(111) system, large, independent domains of the Ge (111)-(3×1) Ag phase were imaged and investigated. Previous studies have reported it only as small insets between Ge (111)-(4×4) Ag and Ge (111)- c (2×8) domains. The transmission electron diffraction data were analyzed using a Direct Methods approach and "heavy-atom holography," with the result of an atomic model of the structure similar to that of Ge (111)-(3×1) Ag .

Electron-diffraction patterns from frozen hydrate protein microcrystals: A new tool instructural studies

1994 ◽  
Vol 52 ◽  
pp. 102-103
Author(s):  
Christoph Burmester ◽  
Kenneth C. Holmes ◽  
Rasmus R. Schröder
Keyword(s):  
Electron Diffraction ◽  
Diffraction Data ◽  
Heavy Atom ◽  
Atomic Resolution ◽  
Protein Crystals ◽  
Electron Diffraction Data ◽  
Phase Information ◽  
Isomorphous Replacement ◽  
Diffraction Patterns

Electron crystallography of 2D protein crystals can yield models with atomic resolution by taking Fourier amplitudes from electron diffraction and phase information from processed images. Imaging at atomic resolution is more difficult than the recording of corresponding electron diffraction patterns. Therefore attempts have been made to recover phase information from diffraction data from 2-D and 3-D crystals by the method of isomorphous replacement using heavy atom labelled protein crystals. These experiments, however, have so far not produced usable phase information, partly because of the large experimental error in the spot intensities. Here we present electron diffraction data obtained from frozen hydrated 3-D protein crystals with an energy-filter microscope and a specially constructed Image Plate scanner which are of considerably better crystallographic quality (as evidenced in much smaller values for the crystallographic R-factors Rsym and Rmerge) than those reported before. The quality of this data shows that the method of isomorphous replacement could indeed be used for phase determination for diffraction data obtained from 3-D microcrystals by electron diffraction.

Multiple isomorphous replacement for phase determination in protein crystals

1995 ◽  
Vol 53 ◽  
pp. 856-857
Author(s):  
Christoph Burmester ◽  
Kenneth C. Holmes ◽  
Rasmus R. Schröder
Keyword(s):  
Electron Diffraction ◽  
Heavy Atom ◽  
Atomic Resolution ◽  
Protein Crystals ◽  
Electron Diffraction Data ◽  
Phase Information ◽  
Electron Dose ◽  
Isomorphous Replacement ◽  
Resolution Electron ◽  
Diffraction Patterns

Electron crystallography of 2D protein crystals can yield models with atomic resolution by taking Fourier amplitudes from electron diffraction and phase information from processed images. Imaging at atomic resolution is more difficult than the recording of corresponding high resolution electron diffraction patterns. Therefore attempts have been made to retrieve phase information from diffraction from heavy atom labelled protein crystals. The expected differences between native and labelled crystals are small, therefore a high experimental accuracy is necessary. This is achieved by the use of energy filter TEM and image plates, as dicussed in. Here we present electron diffraction data obtained from frozen hydrated 3D protein crystals with an energy filter microspcope and a specially designed image plate scanner. Data were recorded for the native crystal as well as for two different heavy atom derivatives. Differences between the native and the derivate forms can be detected and are significant.Electron diffraction patterns from frozen hydrated catalase crystals were recorded on an EFTEM Zeiss 912 Ω (120kV, zero loss mode, energy width ΔE=10eV, electron dose 5 e-/A2) using image plates and a quasi confocal scanner readout.

Maximum Entropy and Bayesian Methods of Solving the Phase Problem in Electron Diffraction

1997 ◽  
Vol 3 (S2) ◽  
pp. 1021-1022
Author(s):  
C.J. Gilmore
Keyword(s):  
Electron Diffraction ◽  
Ab Initio ◽  
Maximum Entropy ◽  
Bayesian Methods ◽  
Diffraction Data ◽  
Heavy Atom ◽  
Electron Diffraction Data ◽  
Data Sets ◽  
List Type ◽  
Wide Range

The phasing of electron diffraction data poses considerable problems for traditional direct or heavy atom crystallographic methods since the data are incomplete or at less than atomic resolution (i.e. 1.1Å), and subject to errors arising from dynamical scattering effects. The Bricogne formalism for phasing diffraction data using maximum entropy (ME) and Bayesian methods has proved especially useful in these situations1 since this formalism is stable irrespective of data resolution and completeness, and is robust with respect to errors on the measured diffraction intensities.Successes with this formalism this include a wide range of structures: (1)The ab initio phasing of diketopiperazine C4H6N2O2 (Fig 1).(2)The structure solution of CuCl2.3Cu(OH)2 (Fig 2).(3)The ab initio phasing of two 2-D membrane data sets at ca. 6Å resolution without the use of image phases (Halorhodopsin and Omp F Porin4 - Figs 3 and 4). In addition, we have had some success in phasing the 3-D data of bacteriorhodopsin at 6Å.

Sign in / Sign up

Export Citation Format

Share Document