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O: Fachverband Oberflächenphysik

O 6: Oxides and Insulator Surfaces: Structure, Epitaxy and Growth

O 6.1: Vortrag

Montag, 17. März 2025, 10:30–10:45, H8

Characterizing Approximants of Oxide Quasicrystals with a Novel Geometric Approach — •Martin Haller, Sebastian Schenk, Stefan Förster, and and Wolf Widdra — Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany

Oxide quasicrystals (OQCs) are aperiodic 2D oxide films exhibiting dodecagonal symmetry, which are grown on hexagonal metal substrates. This dodecagonal symmetry arises from a square-triangle-rhombus tiling, derived from Ba, Sr, or Eu hosted within a Ti-O network [1]. Approximants are periodic structures composed of the same tiling elements, thus exhibiting a close structural relationship to the OQC. Variations in stoichiometry lead to the emergence of different approximant structures, ranging from simple tilings with a triangle:square:rhombus frequency ratio of 4:2:0 to more complex configurations such as the 60:22:8 approximant [2]. In this presentation, we will introduce newly discovered approximant phases identified in the Sr-Ti-O/Pd(111) and Eu-Ti-O/Pd(111) systems through STM and LEED. Specifically, we will discuss two hexagonal approximants with tiling frequency ratios of 20:3:6 and 8:0:3, as well as an oblique 10:3:2 approximant. Additionally, we will apply a novel geometric approach for characterizing the tilings derived from STM data [3]. This innovative method provides a measure in a 4D hyperspace for classifying the relationship of approximants to the parent OQC.
[1] Schenk et al., Nature Communications, 13, 7542 (2022)
[2] Wührl et al., Phys. Rev. B, 107, 195414 (2023)
[3] Imperor-Clerc et al., Phys. Rev. B, 110, 144106 (2024)

Keywords: Quasicrystals; Approximants; Ternary Oxide; STM; LEED