Fluid-like Surface Layer and Its Flow Characteristics in Glassy Nanotubes

TL;DR

This study reveals a fluid-like surface layer in glassy nanotubes that significantly influences their mechanical properties, with the layer exhibiting high viscosity and bond-switching dynamics at room temperature.

Contribution

It demonstrates the existence of a ~1 nm thick fluid-like surface layer in glassy nanotubes and elucidates its impact on their viscoelastic behavior at nanoscale.

Findings

Size-dependent viscoelasticity observed in nanotubes.

Presence of a ~1 nm fluid-like surface layer confirmed.

Surface layer exhibits high viscosity similar to high-temperature glass.

Abstract

We observed strongly size-dependent viscoelasticity in amorphous SiO2 and Si nanotubes with shell thickness down to ~8 nm. A core-shell model shows that a ~1 nm thick fluid-like surface layer has a significant effect on the mechanical behavior of nanotubes and matches well with our experimental results. Surprising, the surface layer exhibits a room temperature viscosity equivalent to that of bulk glass above 1000 C. Additionally, a low activation energy extracted from temperature dependent creep tests indicates that the viscous flow in the surface layer is due to bond motion/switching, instead of bond breaking. These findings unambiguously show the presence of a fluid-like surface layer and elucidate its role on dynamic mechanical behavior in nanoscale inorganic glass.