Berlin 2024 – scientific programme

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DS: Fachverband Dünne Schichten

DS 21: Optical Analysis of Thin Films

DS 21.5: Talk

Friday, March 22, 2024, 11:00–11:15, A 053

Exploring the Tunability of Phonon Properties in Ultra-Thin Bismuth Films — •Felix Hoff¹, Timo Veslin¹, Abdur Rehman Jalil², Peter Kerres², Jonathan Frank¹, Thomas Schmidt¹, Yazhi Xu³, Dasol Kim¹, Riccardo Mazzarello³, and Matthias Wuttig^1,2 — ¹I. Institute of Physics (IA), RWTH Aachen University, Germany — ²Peter Grünberg Institute - JARA-Institute Energy Efficient Information Technology (PGI-10), Germany — ³Dipartimento di Fisica, Sapienza University of Rome, Italy

In recent years, ultra-thin bismuth films have gathered attention for applications in thermoelectrics, ferroelectrics, and recently for topological applications, too. Our study focuses on the systematic exploration of ultra-thin bismuth films, utilizing advanced characterization techniques to unveil the intriguing changes in phonon properties as the layer thickness is reduced. Raman spectroscopy and optical fs pump probe spectroscopy were employed to measure phonon frequencies and lifetimes, exposing a complex interplay of factors influencing the observed hardening and softening of phonon modes. Additional investigations employ XRD, revealing structural modifications and distortions. DFT calculations unravel the intricate relationship between structural changes, chemical bonding, and optical properties. We determine the layer-thickness-dependent dielectric function, which show remarkable confinement effects. Epitaxially grown samples, detailed in a prior publication, ensure reproducibility. Motivated by achieving high-quality thin films, our work contributes to understanding the underlying mechanisms governing phonon properties in ultra-thin bismuth.

Keywords: Coherent Phonons; Bismuth; Femtosecond; Raman; Tunability