Enantiomorphic distribution maps for metals and metal alloys – sciencedaily

Left-handedness or right-handedness is a property of symmetry that many macroscopic objects also exhibit and which is of immense importance, especially for the bioactivity of organic molecules. Chirality is also relevant for physical or chemical properties such as optical activity or enantioselectivity of crystalline solids or their surfaces. In the case of chiral metal phases, unconventional superconductivity and unusual magnetic ordered states are related to the chirality of the underlying crystal structure. Despite this link between chirality and the properties of a material, detection is often difficult because left-handed and right-handed structural variants can cancel each other out or at least weaken the chirality effect.

It is not always possible to prepare chiral materials which contain only one of the two structural variants. Most often, both structural variants are present in a polycrystalline material. For systematic investigations, it is therefore important to be able to determine the laterality with good spatial resolution.

In the present work, it is shown that the EBSD method can be used to determine the distribution of enantiomorphic structural variants not only in multi-component phase polycrystalline materials, but also for the chiral elementary structure β-Mn. The difference between multicomponent crystal structures and elemental structure is therefore of particular importance, since the X-ray diffraction method, which is generally used to determine laterality, does not provide any information on laterality for an elemental structure. chiral such as β-Mn. In recent years, EBSD (Electron Backscatter Diffraction) has been an established method for determining local crystal orientation in a polycrystalline material using Kikuchi lines. The EBSD investigation is performed under a scanning electron microscope. It is therefore a relatively simple method for determining the local crystallographic properties of a polycrystalline material. Kikuchi lines are formed by diffraction of electrons on a steeply inclined flat surface. However, the conventional evaluation methods of the EBSD model do not make it possible to conclude on the laterality of a phase. Only taking into account the dynamic multiple scattering of electrons in the simulation calculations gives differences in the Kikuchi lines of the two enantiomorphs. An assignment of laterality is made based on the best agreement of the experimental EBSD model with one of the two simulated models.

These investigations were carried out on the β-Mn phases and the structurally closely related multicomponent compound Pt2Cu3B. The distribution of enantiomorphs was determined from the EBSD pattern for both phases, while X-ray diffraction on Xenon-FIB (Focused ion beam) cut crystals allowed assignment for the ternary phase only. The EBSD-based determination of the distribution of enantiomorphs in a polycrystalline material greatly simplifies material preparation with a defined hand.

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