Abnormally High Thermal Conductivity in Fivefold Twinned Diamond Nanowires

TL;DR

This study reveals that fivefold twinned diamond nanowires exhibit unexpectedly high thermal conductivity due to phonon hydrodynamics, especially at small cross-sectional areas, challenging traditional views on twinned nanostructures.

Contribution

It demonstrates that fivefold twinned diamond nanowires can have enhanced thermal conductivity through phonon hydrodynamics, contrary to typical deterioration in twinned nanomaterials.

Findings

Thermal conductivity increases sharply as cross-sectional area decreases below 7.1 nm².

5FT-DNWs with minimal cross-section outperform bulk diamond in thermal conductivity.

Phonon hydrodynamics dominate scattering, enabling super-transport in these nanowires.

Abstract

Fivefold twins (5FTs), discovered nearly 200 years ago, are a common multiply twinned structure that usually dramatically deteriorate the thermal transport properties of nanomaterials. Here, we report the anomalous thermal conductivity ($\kappa$) in a novel fivefold twinned diamond nanowires (5FT-DNWs). The $\kappa$ of 5FT-DNWs is effectively enhanced by the defects of 5FT boundaries, and non-monotonically changes with the cross-sectional area ($\textit{S}$). Above the critical $\textit{S}$ = 7.1 nm$^{2}$, 5FT-DNWs show a constant value of $\kappa$, whereas below it, there appears a sharp increase in $\kappa$ with decreasing $\textit{S}$. More importantly, 5FT-DNWs with minimal $\textit{S}$ show a superior $\kappa$ over the bulk diamond. By confirming the Normal-process-dominated scattering event, it is demonstrated that the phonon hydrodynamic behavior plays a determinative role in abnormally high $\kappa$ of 5FT-DNWs with small $\textit{S}$. The super-transported phonon hydrodynamic phenomenon unveiled in the twinned diamond nanowires may provide a new route for pursuing highly thermally conductive nanomaterials.