Anomalous Raman features of silicon nanowires under high pressure

TL;DR

This study reveals that silicon nanowires under high pressure form rigid, anisotropic structures with unique Raman features, showing enhanced mechanical and phononic properties compared to bulk silicon.

Contribution

It demonstrates that silicon nanowires do not amorphize under high pressure but develop distinct phonon confinement and anisotropic structures, revealed through in-situ Raman spectroscopy.

Findings

Splitting of 2TO Raman mode into 2TO(L) and 2TO(W) at >= 5 GPa

Silicon nanowires exhibit increased linear modulus under pressure

Nanowires show less anharmonicity and more localized phonon confinement

Abstract

The potential of silicon nanowires (SiNWs), (diameter < 10 nm) to transform into rigid bundle-like structures with distinct phonon confinement under high pressure (<= 15 GPa), instead of amorphising as per previous reports, is demonstrated using in-situ Raman spectroscopy. The newly observed splitting of the second order transverse optical (2TO) Raman mode into 2TO(L) and 2TO(W) phonon modes at >= 5 GPa establishes a highly anisotropic and mode-dependent pressure response of these SiNWs. Properties of the novel structures are superior compared to other nano-structured silicon and bulk-Si in terms of increased linear modulus, more localized phonon confinement and less anharmonicity.