Regensburg 2019 – scientific programme

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DS: Fachverband Dünne Schichten

DS 7: Optical Analysis of Thin Films II (Reflection, Ellipsometry, Raman, IR-DUV Spectroscopy, ...

DS 7.4: Talk

Monday, April 1, 2019, 15:45–16:00, H32

Optical properties along the pseudo-binary line between Bi2Se3 and Sb2Se3 — •Ludovica Guarneri, Stefan Maier, and Matthias Wuttig — I.Physikalisches Institut (IA), RWTH Aachen University, D-52056 Aachen, Germany

A unique bonding mechanism, coined metavalent bonding (MVB), has recently been introduced. It is characterized by set of unique properties including large optical dielectric constants, high Born effective charges and soft optical modes. It has been identified in a class of inorganic materials including Phase Change Materials, Thermoelectrics and Topological Insulators. In addition, a unique bond breaking mechanism has been found, where MVB materials are characterized by a high probability of multiple events, i.e. several fragments being dislodged by a single laser pulse in atom probe tomography. Such a behavior is not found in materials which utilize ordinary covalent, metallic or ionic bonding. Bi2Se3 and Sb2Se3 show respectively high and low probability of multiple events, which indicates that Bi2Se3 employs MVB, while Sb2Se3 does not. We have thus studied the pseudo-binary line Bi2Se3:Sb2Se3 to investigate how MVB breaks down. To this end, we measure the optical properties using FT-IR spectroscopy between 30 meV and 0.80 eV. In this range, the dielectric function is governed by the electronic polarizability of the valence electrons, allowing to probe chemical bonding. In a narrow stoichiometry range on the Bi-rich side, a significant increase in the dielectric constant upon crystallization is observed. This finding is evidence for the formation of MVB, which confirms that MVB is a distinctive bonding mechanism.