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 Cu64Zr36 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.