Lifetimes of confined acoustic phonons in ultrathin silicon membranes

J. Cuffe, O. Ristow, E. Chávez, A. Shchepetov, P. O. Chapuis, F. Alzina, M. Hettich, M. Prunnila, J. Ahopelto, T. Dekorsy, C. M. Sotomayor Torres

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    74 Citations (Scopus)


    We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ∼4.7 ns to 5 ps with decreasing membrane thickness from ∼194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic surface roughness scattering including a wavelength-dependent specularity. Our results provide insight to understand some of the limits of nanomechanical resonators and thermal transport in nanostructures. © 2013 American Physical Society.
    Original languageEnglish
    Article number095503
    JournalPhysical Review Letters
    Issue number9
    Publication statusPublished - 26 Feb 2013


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