Lifetimes of Confined Acoustic Phonons in Ultrathin Silicon Membranes

Lifetimes of Confined Acoustic Phonons in Ultrathin Silicon Membranes

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...

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Bibliographic Details
Main Authors: Cuffe, John, Ristow, O., Chavez, E., Shchepetov, A., Chapuis, P. O., Alzina, F., Hettich, M., Prunnila, M., Ahopelto, Jouni, Dekorsy, T., Torres, C. M. Sotomayor
Other Authors: Massachusetts Institute of Technology. Department of Mechanical Engineering
Format: Article
Language:en_US
Published: American Physical Society 2013
Online Access:http://hdl.handle.net/1721.1/78653
Description
Summary: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.

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