Five-fold symmetry in Au–Si metallic glass

Abstract

The first metallic glass of Au–Si alloy for over half a century has been discovered, but its atomic structure is still puzzling. Herein, Au₈Si dodecahedrons with local five-fold symmetry are revealed as building blocks in Au–Si metallic glass, and the interconnection modes of Au₈Si dodecahedrons determine the medium-range order. With dimensionality reduction, the surface ordering is attributed to the motif transformation of Au₈Si dodecahedrons into planar Au₅Si pyramids with five-fold symmetry, and thus the self-assembly of Au₅Si pyramids leads to the formation of the ordered Au₂Si monolayer with the lowest energy. Furthermore, structural similarity analysis is performed to unveil the physical origin of the 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.