Tailored nanophononic wavefield in a patterned bilayer system probed by ultrafast convergent beam electron diffraction

Optically excited nanostructures provide a versatile platform for the generation of confined nanophononic fields with potential (non-)linear interactions between different degrees of freedom. Control of resonance frequencies and the selective excitation of acoustic modes still remains challenging due to the interplay of nanoscale geometries and interfacial coupling mechanisms. Here, we demonstrate that a semiconductor membrane patterned with a platinum stripe acts as a tailored source for high-frequency strain waves generating a multi-modal distortion wave propagating through the membrane. To locally monitor the ultrafast structural dynamics at a specific distance from the deposited metal stripe, we employ ultrafast convergent beam electron diffraction in a laser-pump/electron-probe scheme. Experimentally observed acoustic deformations are reproduced by numerical simulations in a continuous medium model, revealing a spatiotemporal evolution of the lattice dynamics dominated by local rotations with minor strain and shear contributions. (C) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommon.org/licence/by/4.0/).

Automated summary

Optically excited nanostructures serve as a versatile platform for generating confined nanophononic fields with potential (non-)linear couplings. In this study, a semiconductor membrane patterned with a platinum stripe was utilized to generate high-frequency strain waves, and the ultrafast structural dynamics were monitored using ultrafast convergent beam electron diffraction. The experimental results were reproduced by numerical simulations, revealing the spatiotemporal evolution of lattice dynamics dominated by local rotations.