Lattice vibrational properties of Si/Ge core-shell nanowires for thermoelectric applications

Using first principles Density Functional Theory (DFT) calculations, we have studied the structural and lattice vibrational properties of [111]-oriented Si/Ge core-shell nanowires. Our results show that the fundamental atomicity of the underlying lattice is important for an accurate explanation of phonon frequencies. The detailed analysis shows that thermal conductance due to selective phonon modes of Si/Ge coreshell nanowires can be suppressed by engineering the ratio of core/shell atoms, as well as the detailed atomistic configuration. In particular, our results reveal that heavier shell atoms in Si/Ge core-shell nanowires reduce thermal conductivity, increasing their thermoelectric figure of merit.