Convergent-beam Electron Diffraction Discs Research Articles

Measurement of strain in silver halide particles by convergent beam electron diffraction

Only limited radiation damage was observed in convergent beam electron diffraction (CBED) patterns obtained at 300 kV with a focussed 10 nm probe from silver halide particles cooled to 100 K. For duplex particles with a coherent interface between the AgBr core and a AgBrI shell, the planar displacements calculated from a spherical isotropic model for the strain field were shown to be consistent with the intensity rocking curves observed in large-angle CBED patterns mapped across a 0.25 micro m particle. A useful analogy with optical Fraunhofer and Fresnel diffraction is the basis for a discussion of the relation between planar displacement and their associated kinematic rocking curves. The sign of the misfit between the core and shell was confirmed by a new method based upon comparison of the elastic and Kikuchi contrast across the boundary of CBED discs.

Observation of accidental Bloch wave degeneracies at zone-axis critical voltages in high-energy electron diffraction

Abstract Observations of both dark-field and bright-field convergent-beam discs were performed close to the zone-axis critical voltages (ZACV) of f.c.c. stainless steel , Si and Cr zone axes. A switching of asymmetric contrast was observed in the dark-field convergent-beam electron diffraction (CBED) discs of each zone-axis pattern. In the case of stainless steel, the switch of asymmetric contrast occurred at different accelerating voltages depending on the choice of diffracted beam. This effect can be interpreted by the structure of the Bloch wave dispersion surfaces. In the case of the Si ZACV, the switching of asymmetric contrast was observed in both bright- and dark-field CBED discs at the ZACV, and the results facilitated a precise determination of the ZACV. The asymmetric contrast was also observed in the dark-field discs of the Cr axis and again facilitated a precise determination of the ZACV.

On-Line Measurement of Foil Thickness from Convergent Beam Electron Diffraction Patterns

Accurate values of foil thickness are required in many materials science applications, such as for measurement of defect concentrations and for x-ray microanalysis absorption corrections. Kelly et al. demonstrated that convergent beam electron diffraction (CBED) patterns can be analyzed using a simple graphical technique to give values for foil thickness with ±2% accuracy. More recently, Allen extended the treatment to make use of both maxima and minima in the CBED disks. The technique requires a knowledge of the d-spacing of the reflection, the electron wavelength, an evaluation of the deviation parameter, si, associated with the i-th fringe in the diffracted beam disk, and the assignment of a set of constants to "index" the fringes.