Dresden 2017 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 39: Thin Film Applications
DS 39.7: Vortrag
Donnerstag, 23. März 2017, 11:00–11:15, CHE 91
Nanoscale picosecond acoustic spectrometry of phononic superlattices — •Dennis Meyer1, Henning Ulrichs1, Florian Döring2, and Hans-Ulrich Krebs2 — 1I. Physikalisches Institut, Universität Göttingen, Germany — 2Institut für Materialphysik, Universität Göttingen, Germany
We show how the characteristics of acoustic resonances in metallic nano-cavities can be tailored by tuning the interplay with an underlying phononic crystal. For this purpose we exploit ultrafast optical excitation, which enables us to address a resonant surface mode with frequency around 180 GHz in a wedge-shaped tungsten thin film, grown on a MgO/ZrO2 phononic crystal. The lifetime of the surface mode was found to vary between 60 and 250 ps, depending on the position on the wedge. Vice versa, one can also regard our results as a demonstration of a nanoscale acoustic spectrometry principle for investigation of the elastic wave band structure of a superlattice: a strong response of the surface layer only appears for frequencies inside an acoustic mini-band gap. By spatially moving the laser across the wedge, the first mini-band gap was mapped out. These results are in good agreement to a theoretical model of the system. In addition to these findings, we see an unexpected increase in frequency in the experimental data, when crossing the lower band-gap edge from above. We acknowledge financial support by the DFG within the CRC 1073 ’Atomic scale control of energy conversion’.