Five-fold symmetry in Au-Si metallic glass

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.