When crystalline solids are confined to the nanometer range, phonon transport within them can be significantly altered due to various effects, namely (i) increased boundary scattering; (ii) changes in phonon dispersion relation; and (iii) quantization of phonon transport. For example, theoretical studies (e.g., Chung et al., 2000) have suggested that, as the diameter of a silicon nanowire (NW) becomes smaller than 20 nm, the phonon dispersion relation, and therefore its density of states, could be modified due to phonon confinement. This in turn impacts the phonon group velocities and scattering rates that can further reduce the thermal conductivity of confined structures.

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