Two-step modification of phonon mean free paths for thermal conductivity predictions of thin-film-based nanostructures

Qing Hao, Yue Xiao, Sien Wang

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


As one simple metamaterial, nanopatterns are often fabricated across a thin film so that the thermal transport can be manipulated. The etched sidewalls for these nanostructures are usually rough due to surface defects introduced during the nanofabrication, whereas the top and bottom film surfaces are smoother. In existing analytical models, the contrast between these surfaces has not been addressed and all boundaries are assumed to be diffusive for phonon reflection. In this paper, a new two-step approach to address this issue is proposed for phonon transport modeling of general thin-film-based structures. In this approach, the effective in-plane phonon mean free paths (ΛFilm) are first modified from the bulk phonon MFPs to account for the influence of the top/bottom film surfaces, with possibly enhanced probability of specular phonon reflection at cryogenic temperatures. This ΛFilm is further modified to include the scattering by etched sidewalls with almost completely diffusive phonon scattering. Such a two-step phonon mean free path modification yields almost identical results as frequency-dependent phonon Monte Carlo simulations for etched nanowires and representative nanoporous thin films. This simple yet accurate analytical model can be applied to general thin-film-based nanostructures to combine the phonon size effects along orthogonal directions.

Original languageEnglish (US)
Article number119636
JournalInternational Journal of Heat and Mass Transfer
StatePublished - Jun 2020
Externally publishedYes


  • Nanoporous thin film
  • Rectangular nanowire
  • Two-step phonon mean free path modification

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes


Dive into the research topics of 'Two-step modification of phonon mean free paths for thermal conductivity predictions of thin-film-based nanostructures'. Together they form a unique fingerprint.

Cite this