One-Dimensional Twisted and Tubular Structures of Zinc Oxide by Semiconductor-Catalyzed Vapor-Liquid-Solid Synthesis

TL;DR

This paper demonstrates that using a semiconductor catalyst like Ge in vapor-liquid-solid synthesis enables the creation of novel twisted and tubular ZnO nanostructures with unique morphologies and high twisting rates.

Contribution

It introduces the use of a semiconductor catalyst for VLS synthesis of ZnO, leading to new twisted and tubular morphologies not achievable with metallic catalysts.

Findings

Twisted nanotubes with hollow cores and high twisting rates were synthesized.

The hollow core results from growth and etching competition at the interface.

Twisting rates suggest elastic softening during growth.

Abstract

The exploration of new catalysts for the vapor-liquid-solid (VLS) synthesis of one-dimensional (1-D) materials promises to yield new morphologies and functionality. Here, we show, for the model ZnO system, that this possible using a semiconductor (Ge) catalyst. In particular, two unusual morphologies are described: twisted nanowires and twisted nanotubes, in addition to the usual straight nanowires. The twisted nanotubes show large hollow cores and surprisingly high twisting rates (up to 9o/{\mu}m), which cannot be easily explained through the Eshelby twist model. A combination of ex situ and in situ transmission electron microscopy measurements suggest that the hollow core results from a competition between growth and etching at the Ge-ZnO interface during synthesis. The twisting rate is consistent with a softening of elastic rigidity. These results indicate that the use of unconventional, nonmetallic catalysts provide opportunities to synthesize unusual oxide structures with potentially useful properties.