Thermal contraction in silicon nanowires at low temperatures

TL;DR

This study theoretically investigates the low-temperature thermal contraction of silicon nanowires in different crystallographic directions, revealing anisotropic effects and the influence of structural ratios on the coefficient of thermal expansion.

Contribution

It provides new insights into the anisotropic thermal contraction behavior of silicon nanowires and how structural ratios affect their thermal expansion at low temperatures.

Findings

All studied SiNWs exhibit thermal contraction at low temperatures.

The CTE in the [110] direction is larger due to anisotropic bending modes.

CTE decreases as the structure ratio increases, remaining negative across temperatures.

Abstract

The thermal expansion effect of silicon nanowires (SiNW) in [100], [110] and [111] directions with different sizes is theoretically investigated. At low temperatures, all SiNW studied exhibit thermal contraction effect due to the lowest energy of the bending vibration mode which has negative effect on the coefficient of thermal expansion (CTE). The CTE in [110] direction is distinctly larger than the other two growth directions because of the anisotropy of the bending mode in SiNW. Our study reveals that CTE decreases with an increase of the structure ratio $\gamma=length/diameter$, and is negative in whole temperature range with $\gamma=1.3$.