title: Lifetimes of confined acoustic phonons in ultrathin silicon membranes.
abstract: 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.
authors.affiliation: Catalan Institute of Nanotechnology (ICN2), Campus UAB, 08193 Bellaterra (Barcelona), Spain. jcuffe@mit.edu
authors.forename: J
authors.initials: J
authors.lastname: Cuffe
authors.forename: O
authors.initials: O
authors.lastname: Ristow
authors.forename: E
authors.initials: E
authors.lastname: Chávez
authors.forename: A
authors.initials: A
authors.lastname: Shchepetov
authors.forename: P-O
authors.initials: PO
authors.lastname: Chapuis
authors.forename: F
authors.initials: F
authors.lastname: Alzina
authors.forename: M
authors.initials: M
authors.lastname: Hettich
authors.forename: M
authors.initials: M
authors.lastname: Prunnila
authors.forename: J
authors.initials: J
authors.lastname: Ahopelto
authors.forename: T
authors.initials: T
authors.lastname: Dekorsy
authors.forename: C M
authors.initials: CM
authors.lastname: Sotomayor Torres
mesh_terms: D000162:Acoustics; D008567:Membranes, Artificial; D008962:Models, Theoretical; D049329:Nanostructures / Q000737:chemistry*; D060739:Phonons; D012825:Silicon / Q000737:chemistry*
chemical_list: D008567:Membranes, Artificial; D012825:Silicon