  Crystallization from an amorphous atomic structure is usually seen as a
spontaneous process in pursuit of a lower energy state, but for alloy systems
it is often hard to elucidate because of the intrinsic structural and
compositional complexity. Here, by means of electron beam irradiation, we found
surface-limited, and thus size-dependent crystallization in a system of
monoatomic Pd metallic glass, which is ascribed to the structural differences
between the surface and the interior. The equilibrium thickness of the surface
crystallization is controllable, presenting a promising approach to fabricate
novel nanostructures. The investigation is believed to provide a general
understanding of solid amorphous-to-crystalline phase transition from the
nanoscale to the bulk size.
