Blocking phonons via nanoscale geometrical design

By introducing a serpentine structure in a straight silicon nanowire, we have experimentally achieved a significant reduction in its phonon thermal conductance at low temperature (T < 5 K.) The magnitude of this effect is one order of magnitude larger than expected based on a thermal resistors picture. With a more refined theoretical model that considers the frequency dependence of phonon transport, we are able to quantitatively account for the experimental results of straight and serpentine nanowires in the whole temperature range. This experimental demonstration of a large, purely geometry induced effect on nanoscale thermal conductance contrasts strikingly with the negligible effects reported on a different nanoscale system in a previous publication.