Control of surface morphology and crystal structure of silicon nanowires and their coherent phonon transport characteristics

We report on the first experimental observation of coherent phonon transport characteristics in silicon nanowires (SiNWs) synthesized by a one-step surface reconstruction growth mechanism. As-grown SiNWs taper down along the growth direction alongside a decrease in both roughness and stacking fault density. Furthermore, by systematically measuring the temperature-dependent thermal conductivity using a conventional thermal bridge method, we found that the measured thermal conductivity values of surface-reconstructed (SR)-SiNWs (13-20 W m−1 K−1) at room temperature are markedly lower than that predicted from the conventional diffuse phonon transport model for given NW diameters. We also observed that the thermal conductivities of SR-SiNWs exhibit an unexpected power law of ∼Tα (1.6 ⩽ α ⩽ 1.9) in the temperature range of 25-60 K, which cannot be explained by the typical Debye ∼ T3 behavior. Interestingly, our experimental results are consistent with a frequency-dependent model, which can be induced by coherence in the diffuse reflection and backscattering of phonons at the rough surface and stacking faults on SR-SiNWs, resulting in the suppressed thermal conductivity. Therefore, the demonstrated rational synthesis model and measurement technique promise great potential for improving the performance of a wide range of one-dimensional NW-based thermoelectric devices.