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Using large scale molecular dynamics simulations, we study the thermalconductivity of bare and surface passivated silicon nanowires (SiNWs). For thesmaller cross-sectional widths $w$, SiNWs become unstable because of thesurface amorphousization and even evaporation of a certain fraction of Si atomswhen $w \leq 2$ nm. Our results suggest that the surface (in--)stability isrelated to a large excess energy $\Delta$ of the surface Si atoms with respectto the bulk Si. This is because the surface Si atoms being less coordinated andhaving dangling bonds. As a first step of our study, we propose a practicallyrelevant method that uses $\Delta$ as a guiding tool to passivate thesedangling bonds and thus stabilizes SiNWs. The surface stabilization is achievedby passivation of Si atoms by hydrogen or oxygen. These passivated SiNWs arethen used for the calculation of the thermal conductivity coefficient $\kappa$.While the expected trend of $\kappa \propto w$ is observed for all SiNWs,surface passivation provides an added flexibility of tuning $\kappa$ with thesurface coverage concentration $c$ of passivated atoms. Analyzing the phononband structures via spectral energy density, we discuss separate contributionsfrom the surface and the core to $\kappa$. The effect of passivation on SiNWstiffness is also discussed.

Tuning the thermal conductivity of silicon nanowires by surface passivation