Atomistic modeling of the phonon dispersion and lattice properties of free-standing <100> Si nanowires

TL;DR

This paper models phonon dispersion in <100> silicon nanowires using an atomistic force field, revealing how confinement affects their vibrational and thermal properties.

Contribution

It introduces a modified valence force field model that accurately replicates bulk silicon phonons and explores phonon confinement effects in nanowires.

Findings

Phonon dispersion shows strong confinement effects.

Sound velocity and thermal conductance decrease with size.

Specific heat increases due to phonon confinement.

Abstract

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 (Vsnd) and the lattice thermal conductance (kl) decrease as the wire cross-section size is reduced whereas the specific heat (Cv) increases due to increased phonon confinement and surface-to-volume ratio (SVR).