Atomistic modeling of the phonon dispersion and lattice properties of free-standing (100) Si nanowires

Phonon dispersions in (100) silicon nanowires (SiNW) are modeled using a Modified Valence Force Field (MVFF) method based on atomistic force constants. The model replicates the bulk Si phonon dispersion very well. In SiNWs, apart from four acoustic like branches, a lot of flat branches appear indicating strong phonon confinement in these nanowires and strongly affecting their lattice properties. The sound velocity (V_snd) and the lattice thermal conductance K_l decrease as the wire cross-section size is reduced whereas the specific heat (C_ν) increases due to increased phonon confinement and surface-to-volume ratio (SVR).