Journal
STRUCTURAL DYNAMICS-US
Volume 8, Issue 3, Pages -Publisher
AIP Publishing
DOI: 10.1063/4.0000079
Keywords
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Funding
- Volkswagen Foundation as part of the Lichtenberg Professorship Ultrafast nanoscale dynamics probed by time-resolved electron imaging
- Collaborative Research Center Atomic Scale Control of Energy Conversion [DFG-SFB 1073]
- German Academic Scholarship Foundation
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Ultrafast structural probing has improved our understanding of the coupling between atomic motion and electronic/phononic degrees-of-freedom in quasi-bulk materials. By studying the low-frequency acoustic phonon spectrum in metal/semiconductor bilayer systems, it is found that elastic mismatch between materials significantly affects acoustic resonance frequencies.
Ultrafast structural probing has greatly enhanced our understanding of the coupling of atomic motion to electronic and phononic degrees-of-freedom in quasi-bulk materials. In bi- and multilayer model systems, additionally, spatially inhomogeneous relaxation channels are accessible, often governed by pronounced interfacial couplings and local excitations in confined geometries. Here, we systematically explore the key dependencies of the low-frequency acoustic phonon spectrum in an elastically mismatched metal/semiconductor bilayer system optically excited by femtosecond laser pulses. We track the spatiotemporal strain wave propagation in the heterostructure employing a discrete numerical linear chain simulation and access acoustic wave reflections and interfacial couplings with a phonon mode description based on a continuum mechanics model. Due to the interplay of elastic properties and mass densities of the two materials, acoustic resonance frequencies of the heterostructure significantly differ from breathing modes in monolayer films. For large acoustic mismatch, the spatial localization of phonon eigenmodes is derived from analytical approximations and can be interpreted as harmonic oscillations in decoupled mechanical resonators.
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