1. Tuning the thermal conductivity of silicon nanowires by surface passivation
- Author
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Ruscher, Céline, Cortes-Huerto, Robinson, Hannebauer, Robert, Mukherji, Debashish, Nojeh, Alireza, and Phani, A. Srikantha
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
Using large scale molecular dynamics simulations, we study the thermal conductivity of bare and surface passivated silicon nanowires (SiNWs). For the cross-sectional widths $w \le 2$ nm, SiNWs become unstable because of the surface amorphosization and also due to the evaporation of a certain fraction of Si atoms. The observed surface (in-)stability is related to a large excess energy $\Delta$ of the surface Si atoms with respect to the bulk Si, resulting from the surface atoms being less coordinated and having dangling bonds.We first propose a practically relevant method that uses $\Delta$ as a guiding tool to passivate these dangling bonds with hydrogen or oxygen, stabilizing the SiNWs. These passivated SiNWs are used to calculate 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 the surface coverage concentration $c$ of passivated atoms.Indeed, with respect to the bulk $\kappa$, passivation of SiNW reduces $\kappa$ by 75-80\% for $c \to 50\%$ and recovers again by 50\% for the fully passivated samples. Analyzing the phonon band structures via spectral energy density, we discuss separate contributions from the surface and the core to $\kappa$. Our results also reveal that surface passivation increases SiNW stiffness, contributing to the tunability in $\kappa$.
- Published
- 2023