Thermal transport in nanostructured and disordered systems
I will present several examples in which nanostructuration and/or disorder play a relevant role in phonon conductance. The first case is devoted to 3ω measurements in SiGe graded superlattices and how these materials can efficiently suppress phonon transmission across the whole spectrum by simultaneously incorporating scattering mechanisms present in SLs and alloys. The effect is remarkable and has been used to reduce the thermal conductivity below the thin film alloy limit even for thick superlattices with long SL periods
[1]. Then I will show measurements on Si ultrathin membranes and porous Si nanowires using suspended structures. In the case of the NWs we observe a dependence of the thermal conductivity on the diameter and link this observation with the anisotropic etching that occurs during their fabrication
[2]. The last example is devoted to the study of thermal transport (both in-plane, 3ω -Volklein and out-of-plane, 3ω) in disordered organic materials
[3]. I will show that the molecular packing anisotropy that exist in vapor-deposited thin film glasses of an organic semiconductor has a strong impact on heat propagation. In all three examples experimental data is contrasted with molecular or lattice dynamics simulations to unveil the microscopic origin of heat transport.
[1] Ferrando-Villalba et al. Nano Research 8, 2833-2841 (2015) & The Journal of Physical Chemistry C 124, 36, 19864–19872, 2020.
[2] Ferrando-Villalba et al. Scientific reports, 8(1), 12795 (2018).
[3] Ràfols-Ribé et al. Phys. Rev. Mat. 2(3), 035603, (2018) & Ferrando-Villalba, et al. Phys. Rev. Appl. 12(1), 014007, (2019).