The mechanisms responsible for phonon thermal transport at the nanoscale are studied via 3 omega measurements of thermal conductance of nanowire and membrane (0.3K-300K). These measurements illustrate the importance of various characteristic lengths: phonon mean free path, dominant phonon wave length, surface roughness. The general objective rely on heat manipulation at the nanoscale knowing that understanding phonon transport at the nanoscale is one of the most difficult experimental challenges of current mesoscopic physics. The thermal conductance of suspended silicon nanowire and silicon nitride membranes is measured from low temperature to high temperature. Since 2009, we have demonstrated that the thermal transport is dominated by phonon scattering on the surface. We used the presence of ballistic phonon transport at low temperature to reduce thermal conductance by doing nano-engineering of the phonon conductor. This reduction of thermal transport is of high interest for the increasing of the thermoelectric efficiency in nanostructured materials, as described below.

Serpentine section in a silicon nanowire (left). Thermal conductances (right) show reduced thermal conductance in serpentine nanowires, illustrating blocking of heat transfer.

More details here (pdf)

C. Blanc, A. Rajabpour, S. Volz, T. Fournier, and O. Bourgeois "Phonon Heat Conduction in Corrugated Silicon Nanowires Below the Casimir Limit", Appl. Phys. Lett. 103, 043109 (2013). (pdf)

J-S. Heron, C. Bera, T. Fournier, N. Mingo, and O. Bourgeois "Blocking phonons via nanoscale geometrical design", Phys. Rev. B 82, 155458 (2010). (Virtual Journal of Nanoscale Science and Technology, 22, 20, November 8, 2010). (link)

J.-S. Heron, T. Fournier, N. Mingo and O. Bourgeois "Mesoscopic surface effects on the phonon transport in silicon nanowire", Nano Letters 9, 1861 (2009). (link)

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