Lifetimes of Confined Acoustic Phonons in Ultra-Thin Silicon Membranes

John Cuffe (1) , Emigdio Chávez (1) , Pierre-Olivier Chapuis (1, 2) , Francesc Alzina (1) , Oliver Ristow (3) , Andrey Shchepetov (4, 5) , Mike Hettich (3) , Thomas Dekorsy (3) , Clivia M. Sotomayor Torres (1) , Mika Prunnila (5) , Jouni Ahopelto (5)

1 ICN2 - ICN2 - Institut Catala de Nanociencia i Nanotecnologia
2 CETHIL - Centre d'Energétique et de Thermique de Lyon
3 Universität Konstanz
4 IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520
5 VTT - VTT Technical Research Centre of Finland

We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultra-thin 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 \sim 4.7 ns to 5 ps with decreasing membrane thickness from \sim 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.

Domaines: Autre [cond-mat.other]; Acoustique [physics.class-ph]

John Cuffe, Emigdio Chávez, Pierre-Olivier Chapuis, Francesc Alzina, Oliver Ristow, et al.. Lifetimes of Confined Acoustic Phonons in Ultra-Thin Silicon Membranes. Physical Review Letters, 2013, 110 (9), pp.095503. ⟨10.1103/PhysRevLett.110.095503⟩. ⟨hal-00732483⟩