### Filtern

#### Dokumenttyp

- Zeitschriftenartikel (18)
- Beitrag zu einem Tagungsband (4)
- Vortrag (2)

#### Schlagworte

- Electron backscatter diffraction (11)
- EBSD (8)
- Kikuchi patterns (4)
- Simulation (4)
- Cross-correlation (2)
- Dynamical simulation (2)
- Friedel's rule (2)
- GaP (2)
- Kikuchi pattern (2)
- Non-centrosymmetry (2)

#### Organisationseinheit der BAM

Crystal structures that show a broken symmetry in their cubic and hexagonal modifications are of great relevance for optoelectronic and photonic applications. This is why methods which are sensitive to non-centrosymmetric structures are important for analysis of these materials in technological applications.

EBSD is nowadays a common technique for the characterization of crystalline microstructures in scanning electron microscopy. The diffraction patterns are often interpreted by superimposing individual Kikuchi bands which are geometrically described by band edges derived from Braggs law. For the typically very simple crystal structures of technically applied materials, such a simplification of the Kikuchi pattern interpretation works sufficiently well, especially for orientation determinations as a main application of EBSD. The more complex crystal structures, however, are a challenge for EBSD indexing routines which in such cases often fail unpredictably. The use of only the intensities of single reflectors for a description of the Kikuchi band intensity and as a cut-off criterion for a pre-selection of the strongest bands are not satisfactory. Often the result will match too many phases, or there are certain deviations in the intensity prediction which must be adapted manually. This is already problematic if one is absolutely sure that the patterns are originating from the expected phase and it becomes a very questionable procedure for an unknown phase.

We demonstrate polarity-sensitive orientation mapping of non-centrosymmetric phases by Electron Backscatter Diffraction (EBSD). The method overcomes the restrictions of kinematic orientation determination by EBSD, which is limited to the centro-symmetric Laue-groups according to Friedel's rule. Using polycrystalline GaP as an example, we apply a quantitative pattern matching approach based on simulations using the dynamical theory of electron diffraction. This procedure results in a distinct assignment of the local orientation according to the non-centrosymmetric point group of the crystal structure under investigation.

Dynamical simulation of electron backscatter diffraction (EBSD) patterns of imperfect crystals
(2012)

Analysis of Kikuchi band contrast reversal in electron backscatter diffraction patterns of silicon
(2010)

We analyze the contrast reversal of Kikuchi bands that can be seen in electron backscatter diffraction (EBSD) patterns under specific experimental conditions. The observed effect can be reproduced using dynamical electron diffraction calculations. Two crucial contributions are identified to be at work: First, the incident beam creates a depth distribution of incoherently backscattered electrons which depends on the incidence angle of the beam. Second, the localized inelastic scattering in the outgoing path leads to pronounced anomalous absorption effects for electrons at grazing emission angles, as these electrons have to go through the largest amount of material. We use simple model depth distributions to account for the incident beam effect, and we assume art exit angle dependent effective crystal thickness in the dynamical electron diffraction calculations. Very good agreement is obtained with experimental observations for silicon at 20 key primary beam energy.

We discuss the application of EBSD for the analysis of structural features of magnetite and hematite relevant in the topotactic growth of both phases. The orientation relationships of both phases are investigated using characteristically related sets of Kikuchi patterns, which were collected from topotactically intergrown hematite variants and their parent magnetite crystal grain. We address the hexagonal description of trigonal and cubic phases with respect to crystallographic relationships. The combination of locally resolved EBSD measurements and microstructural investigations thus offers a promising opportunity to evaluate orientation relationships and intergrowth between magnetite and hematite.

The kinetic energy of keV electrons backscattered from a rutile (TiO2) surface depends measurably on the mass of the scattering atom. This makes it possible to determine separately the angular distribution of electrons backscattered elastically from either Ti or O. Diffraction effects of these backscattered electrons inside the rutile crystal lead to the formation of Kikuchi patterns. The element-resolved Kikuchi patterns of Ti and O differ characteristically, but each can be described fairly well in terms of the dynamical theory of diffraction. Qualitatively, much of the differences can be understood by considering the relative arrangement of the Ti and O atoms with respect to planes defined by the crystal lattice.