Formation of multilayer structure in metallic glass nanospheres

Atomic structure is a crucial part for the structure–property relations in fabrication and utilization of nanoscale particles. Different from the widely known one-layer core–shell model in crystalline nanoparticles, we report here a multilayer atomic structure formed in metallic glass nanoparticles. The multilayers are characterized by density modulations along the radial direction, while the underlying atomic structure still remains amorphous. As an example, the Cu 64 Zr 36 metallic glass nanospheres are investigated under a wide range of temperatures and sizes using molecular dynamics simulation. We found that the homogeneous amorphous structure undergoes a transition from a single surface core–shell structure to a multilayer structure with a well-defined one-dimensional periodicity when the particles are cooled through the glass transition. This unique layered atomic packing is closely correlated to the variation of the internal stress induced by the surface stress. The layered structure is also accompanied by the property modulation as well as chemical segregation on surface regions. Impact statement Metallic glasses (MGs) are considered as homogeneous and disordered without any long-range atomic packing. Here, we report the development of the onion-like, multilayered atomic structure with a one-dimensional spherical periodic order along the radial direction in MG spheres. The layering transition occurs spontaneously as driven by the surface tension at all ranges of temperatures below the glass-transition temperature. The ordering depends on the radius of the spheres, ranging from a few atomic layers in the large spheres to fully ordered in the smaller ones. The ordering phenomenon is a rare demonstration of the liquid-like behavior in the amorphous solid that blurs the boundary between the solid and liquid in nanoscales. In particular, the multilayered structure could be used in developing functional catalysts and friction or wear-resistant materials. Graphical abstract The formation of the multlayers in MG nanoparticles is measured by the mass density profiles along the radial direction. The one-dimensional ordering depends on the radius of the spheres, ranging from a few atomic layers in the large spheres to fully ordered in the smaller ones. The mass-density profiles, ρ( r ), for the MG spheres with a radius of (a) r = 20 Å, (b) 40 Å, (c) 60 Å, and (d) 120 Å at 700 K. The black squares denote the total density, the filled red up-pointing and blue