scholarly journals Determination of Structure Factors of Al2O3 by means of Large Angle Convergent Beam Electron Diffraction

1995 ◽  
Vol 36 (11) ◽  
pp. 1344-1348 ◽  
Author(s):  
Yoshitugu Tomokiyo ◽  
Takeharu Kuroiwa ◽  
Yasunori Hayashi
Keyword(s):  
Electron Diffraction ◽  
Large Angle ◽  
Convergent Beam Electron Diffraction ◽  
Beam Electron ◽  
Structure Factors ◽  
Convergent Beam

scholarly journals Determination of structure factors of copper by convergent beam electron diffraction

1993 ◽  
Vol 51 ◽  
pp. 688-689
Author(s):  
John Mansfield ◽  
Martin Saunders ◽  
George Burgess ◽  
David Bird ◽  
Nestor Zaluzec
Keyword(s):  
Electron Diffraction ◽  
National Laboratory ◽  
Pure Copper ◽  
Argonne National Laboratory ◽  
Convergent Beam Electron Diffraction ◽  
Beam Electron ◽  
Structure Factors ◽  
Convergent Beam ◽  
Ray Methods

There has been considerable recent interest in the determination of structure factors from convergent-beam electron diffraction (CBED) patterns and the ultimate goal is the ability to retrieve the crystal structure of an unknown crystal by inversion of a CBED pattern. There are a number of different methods that have been used to extract structure factor information. The zone-axis pattern fitting technique of Bird and Saunders has recently been used to obtain structure factors for silicon that compare well with those obtained by X-ray methods. This work extends the techniques to f.c.c. metals, specifically copper.CBED patterns were recorded from [110] zone axes of electropolished foils of pure copper (99.999% purity) in the Philips EM420T at Argonne National Laboratory. The patterns were energy-filtered by scanning the whole pattern across the entrance aperture of a Gatan #607 serial energy loss spectrometer and collecting the zero loss intensity only (energy window ∼5eV).

Large-angle convergent-beam electron-diffraction study of coherent precipitates and decorated dislocations

1996 ◽  
Vol 54 ◽  
pp. 1002-1004
Author(s):  
J.M.K. Wiezorek ◽  
H.L. Fraser
Keyword(s):  
Electron Diffraction ◽  
Angular Resolution ◽  
Large Angle ◽  
Electron Diffraction Study ◽  
Convergent Beam Electron Diffraction ◽  
Crystal Defects ◽  
High Angular Resolution ◽  
Beam Electron ◽  
Diffraction Plane ◽  
Convergent Beam

Conventional methods of convergent beam electron diffraction (CBED) use a fully converged probe focused on the specimen in the object plane resulting in the formation of a CBED pattern in the diffraction plane. Large angle CBED (LACBED) uses a converged but defocused probe resulting in the formation of ‘shadow images’ of the illuminated sample area in the diffraction plane. Hence, low-spatial resolution image information and high-angular resolution diffraction information are superimposed in LACBED patterns which enables the simultaneous observation of crystal defects and their effect on the diffraction pattern. In recent years LACBED has been used successfully for the investigation of a variety of crystal defects, such as stacking faults, interfaces and dislocations. In this paper the contrast from coherent precipitates and decorated dislocations in LACBED patterns has been investigated. Computer simulated LACBED contrast from decorated dislocations and coherent precipitates is compared with experimental observations.

A study of twinning in YBa2Cu3O7−x by large-angle convergent-beam electron diffraction

1990 ◽  
Vol 48 (4) ◽  
pp. 20-21
Author(s):  
P.A. Midgley ◽  
R. Vincent ◽  
D. Cherns
Keyword(s):  
Electron Diffraction ◽  
Oxygen Atom ◽  
Strain Field ◽  
Large Angle ◽  
Convergent Beam Electron Diffraction ◽  
Orthorhombic Distortion ◽  
Beam Electron ◽  
Resultant Powder ◽  
Convergent Beam ◽  
Mesh Grid

The oxygenation of YBa2Cu3O7−x (YBCO) leads to an orthorhombic distortion of the unit cell to accommodate the extra oxygen atom. This makes the formation of twins energetically favourable with CuO4 planar unit chains running alternately along the a and b axes of the parent tetragonal structure. The geometry of this twinning is such that four possible twin variants may co-exist with the twin boundaries lying in the (110) or (110) planes of the deformed structure. The traces of these planes are not mutually perpendicular and thus the crystal is strained to allow for the mismatch. It is to the nature of this strain field that this work has been addressed.Sintered samples were prepared by crushing and dispersing the resultant powder onto a very fine Cu mesh grid. Single crystals were chemically thinned to perforation. No discernible artefacts were seen and similar results were obtained with either method.

Three-phase structure invariants and structure factors determined with the quantitative convergent-beam electron diffraction method

1999 ◽  
Vol 55 (2) ◽  
pp. 188-196 ◽  
Author(s):  
R. Høier ◽  
C. R. Birkeland ◽  
R. Holmestad ◽  
K Marthinsen
Keyword(s):  
Electron Diffraction ◽  
Phase Structure ◽  
Diffraction Method ◽  
Convergent Beam Electron Diffraction ◽  
Beam Electron ◽  
Structure Factors ◽  
Refinement Method ◽  
Three Phase ◽  
Phase Sensitive ◽  
Convergent Beam

Quantitative convergent-beam electron diffraction is used to determine structure factors and three-phase structure invariants. The refinements are based on centre-disc intensities only. An algorithm for parameter-sensitive pixel sampling of experimental intensities is implemented in the refinement procedure to increase sensitivity and computer speed. Typical three-beam effects are illustrated for the centrosymmetric case. The modified refinement method is applied to determine amplitudes and three-phase structure invariants in noncentrosymmetric InP. The accuracy of the results is shown to depend on the choice of the initial parameters in the refinement. Even unrealistic starting assumptions and incorrect temperature factor lead to stable results for the structure invariant. The examples show that the accuracy varies from 1 to 10° in the electron three-phase invariants determined and from 0.5 to 5% for the amplitudes. Individual phases could not be determined in the present case owing to spatial intensity correlations between phase-sensitive pixels. However, for the three-phase structure invariant, stable solutions were found.

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