title: Investigation of phonon coherence and backscattering using silicon nanomeshes.
abstract: Phonons can display both wave-like and particle-like behaviour during thermal transport. While thermal transport in silicon nanomeshes has been previously interpreted by phonon wave effects due to interference with periodic structures, as well as phonon particle effects including backscattering, the dominant mechanism responsible for thermal conductivity reductions below classical predictions still remains unclear. Here we isolate the wave-related coherence effects by comparing periodic and aperiodic nanomeshes, and quantify the backscattering effect by comparing variable-pitch nanomeshes. We measure identical (within 6% uncertainty) thermal conductivities for periodic and aperiodic nanomeshes of the same average pitch, and reduced thermal conductivities for nanomeshes with smaller pitches. Ray tracing simulations support the measurement results. We conclude phonon coherence is unimportant for thermal transport in silicon nanomeshes with periodicities of 100 nm and higher and temperatures above 14 K, and phonon backscattering, as manifested in the classical size effect, is responsible for the thermal conductivity reduction.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Mechanical and Aerospace Engineering, University of California, Irvine, California 92697, USA.
authors.forename: Jaeho
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.|Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Woochul
authors.initials: W
authors.lastname: Lee
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, California 94720, USA.
authors.forename: Geoff
authors.initials: G
authors.lastname: Wehmeyer
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Dhuey
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Deirdre L
authors.initials: DL
authors.lastname: Olynick
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Stefano
authors.initials: S
authors.lastname: Cabrini
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, California 94720, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Dames
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Urban
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA.|Kavli Energy NanoScience Institute, Berkeley, California 94720, USA.
authors.forename: Peidong
authors.initials: P
authors.lastname: Yang