Five-fold Symmetry in Au-Si Metallic Glass

TL;DR

This study uncovers the atomic structure of Au-Si metallic glass, revealing five-fold symmetric Au 8 Si dodecahedrons as fundamental building blocks and explaining the formation of ordered surface layers through motif transformation.

Contribution

It identifies the local five-fold symmetric Au 8 Si dodecahedrons as key structural units in Au-Si metallic glass and explains surface ordering via motif transformation.

Findings

Au 8 Si dodecahedrons are the building blocks of Au-Si metallic glass.

Surface ordering results from motif transformation into Au 5 Si pyramids.

The amorphous nature is due to a smooth energy landscape.

Abstract

The first metallic glass of Au-Si alloy has been discovered for over half a century, but its atomic structure is still puzzling. Herein, Au 8 Si dodecahedrons with local five-fold symmetry are revealed as building blocks in Au-Si metallic glass, and the interconnection modes of Au 8 Si dodecahedrons determine the medium-range order. With dimensionality reduction, the surface ordering is attributed to the motif transformation of Au 8 Si dodecahedrons into planar Au 5 Si pyramids with five-fold symmetry, and thus the self-assembly of Au 5 Si pyramids leads to the formation of the ordered Au 2 Si monolayer with the lowest energy. Furthermore, the structural similarity analysis is performed to unveil the physical origin of structural characteristics in different dimensions. The amorphism of Au-Si is due to the smooth energy landscape around the global minimum, while the ordered surface structure occurs due to the steep energy landscape.