Heat transport in disordered network forming materials: Size effects and existence of propagative modes

Thuy-Quynh Duong , Carlo Massobrio , Mauro Boero , Guido Ori , Évelyne Martin (1, 2)

1 IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520
2 PHYSIQUE - IEMN - Physique - IEMN

We show that in nanoscale disordered networks the thermal conductivity reduces with respect to the bulk value in a way remindful of the analogous behavior in nanocrystalline systems. Our rationale is based on the analogy with nanostruc-tured crystalline silicon and is substantiated by results obtained (experimen-tally, analytically and by atomic scale modelling) on crystalline Si, amorphous Si, glassy SiO 2 and glassy GeTe 4. We point out the implication of such findings on the potential performances of nanoscale heat devices. Thermal transport by conduction in non-metallic materials is due to heat carriers that either propagate with a wave vector (propagons) or that are extended but have no wave vector (diffusons) [1]. Propagons are sensitive to size reduction, diffusons are not. In crystals, the role of propagons is played by phonons travelling undisturbed without undergoing collisions (i.e. ballistically) 5 on a mean free path (MFP) until they experience a scattering (diffusive) event. In a bulk crystalline system, diffusive events are unavoidable regardless of the extent of the largest MFP. This picture changes drastically when a material has nanoscale dimensions, as in a film or a wire for example, these changes being

Mots clés: Thermal conductivity; Disordered materials; Nanoscale effects

Domaines: Physique [physics]; Matière Condensée [cond-mat]

Thuy-Quynh Duong, Carlo Massobrio, Mauro Boero, Guido Ori, Évelyne Martin. Heat transport in disordered network forming materials: Size effects and existence of propagative modes. Computational Materials Science, 2020, 177, pp.109607. ⟨10.1016/j.commatsci.2020.109607⟩. ⟨hal-02990579⟩