Absolute Structure from Scanning Electron Microscopy

Abstract

the absence of centrosymmetry in chiral and polar crystal structures is the reason for many technical relevant physical properties like optical birefringence or ferroelectricity. other chirality related properties that are actually intensively investigated are unconventional superconductivity or unusual magnetic ordering like skyrmions in materials with B20 structure. Despite the often close crystal structure -property relation, its detection is often challenging due to superposition of domains with different absolute structure e.g. chirality. Our investigations of high quality CoSi crystals with B20 structure by both complementary methods X-ray (volume sensitive) and electron backscatter diffraction (EBSD) (surface sensitive) results the consistent assignment of the chirality and reveal fundamental differences in their sensitivity to chirality. The analysis of the surface of a CoSi crystal with domains of different chirality show the high spatial resolution of this method which opens the possibility to analyze the chirality in microstructures of technical relevant materials like thin films and catalysts.

Assignment of enantiomorphs for the chiral allotrope β-Mn by diffraction methods

“…In the Kikuchi pattern analyses presented below, the values are r sim ≈ 0.90 (Pt 2 Cu 3 B) and r sim ≈ 0.96 (β-Mn), which can be considered as sufficiently large for experimental observation. Reliable assignment of the enantiomorphs from experimental Kikuchi patterns by the cross-correlation method are realized for |Δ r | ≥ 0.01 at r m ≥ 0.5 in previous investigations under similar measurement conditions ( 16 , 18 ).…”

“…A large average value r m indicates a good fit of the experimental Kikuchi pattern to the simulated data, while a simultaneous large difference |∆ r | indicates a reliable discrimination among the enantiomorphs. Reliable assignment of the absolute structure from the EBSD pattern demands substantially better match of the experimental pattern with one of the simulated patterns, with |∆ r | ≥ 0.01 and high-quality, experimental pattern fulfilling the condition r m ≥ 0.5 ( 16 , 28 , 32 ).…”

“…A combination of x-ray diffraction and EBSD analysis previously introduced for the chiral CoSi phase ( 16 ) is applied to investigate polycrystalline materials of Pt 2 Cu 3 B and β-Mn. Preliminary EBSD studies on β-Mn are reported in ( 27 ).…”

Kikuchi pattern simulations of backscattered and transmitted electrons

“…This concerns, for example, the discrimination of pseudo-symmetric pattern variants, which can be difficult to detect by conventional EBSD system software. Investigations of this type include the effects of polarity, 7,8 chirality [9][10][11][12] or the correct orientation of tetragonal or other low-symmetry structure variants. [13][14][15] Phase differentiation is discussed in Ref.…”

Polarity Determination in EBSD Patterns Using the Hough Transformation

“…Crystals with non-centrosymmetric structures show Kikuchi bands with asymmetric intensities (Baba-Kishi, 1991, 2002Nolze et al, 2015;Winkelmann & Nolze, 2015). Comparing simulations using the dynamic theory of electron diffraction with experimental patterns shows systematic intensity shifts in the intensity profile over the Kikuchi bands and can be used to reliably determine which atomic layer is responsible for which intensity in an asymmetric Kikuchi band and hence calibrate the pattern (Burkhardt et al, 2020(Burkhardt et al, , 2021. These shifts depend on the atomic arrangement within a crystal lattice (Nolze et al, 2015;Winkelmann & Nolze, 2015).…”