Shape and orientation effects on the ballistic phonon thermal properties of ultra-scaled Si nanowires

TL;DR

This study investigates how the shape, size, and orientation of ultra-scaled Silicon nanowires influence their ballistic phonon thermal properties, revealing universal scaling laws and potential for thermal property engineering.

Contribution

It introduces a comprehensive analysis of geometrical and orientational effects on Si nanowires' thermal properties using a Modified Valence Force Field model, uncovering universal scaling laws.

Findings

C_v increases as cross-section size decreases

Triangular wires have the highest specific heat due to surface-to-volume ratio

Square [110] wires exhibit maximum ballistic thermal conductance

Abstract

The effect of geometrical confinement, atomic position and orientation of Silicon nanowires (SiNWs) on their thermal properties are investigated using the phonon dispersion obtained using a Modified Valence Force Field (MVFF) model. The specific heat ($C_{v}$) and the ballistic thermal conductance ($\kappa^{bal}_{l}$) shows anisotropic variation with changing cross-section shape and size of the SiNWs. The $C_{v}$ increases with decreasing cross-section size for all the wires. The triangular wires show the largest $C_{v}$ due to their highest surface-to-volume ratio. The square wires with [110] orientation show the maximum $\kappa^{bal}_{l}$ since they have the highest number of conducting phonon modes. At the nano-scale a universal scaling law for both $C_{v}$ and $\kappa^{bal}_{l}$ are obtained with respect to the number of atoms in the unit cell. This scaling is independent of the shape, size and orientation of the SiNWs revealing a direct correlation of the lattice thermal properties to the atomistic properties of the nanowires. Thus, engineering the SiNW cross-section shape, size and orientation open up new ways of tuning the thermal properties at the nanometer regime.