Fig. 4: Transition between collective and individual atomic transport.
a The two possible mechanisms for BMG deformation at the nano-scale, viscous flow, L(d) ∝ d (Eq. (1)) and interface diffusion, L(d) ∝ d −1/2 (Eq. (2)), where L is the molding length and d is the molding diameter, exhibit qualitatively and quantitatively different scaling of L(d). b Within viscous flow, different elements have identical velocity of motion (depending on the location relative to the center of the nanocavity), resulting in collective atomic transport with an unchanging and uniform composition along the nanowire. In contrast within the interface diffusion mechanism, elements move with different velocities, according to their different diffusivities in an individual atomic transport process. As more atoms of the faster diffuser reach the tip of the nanowire, the composition of the nanowire changes away from the nominal composition in the feedstock towards that of the faster diffuser. c For a highly optimized BMG composition like the here used Ni45Pd35P16B4, a change in composition generally shorten the time to reach crystallization (τcry (T, c)). Under conditions leading to collective atomic transport (red boxes, viscous flow), the BMG nanowire maintains its composition, hence leaving τcry unchanged. Therefore, if the processing time texp <τcry, crystallization does not take place during deformation and an amorphous nanowire forms. Under conditions leading to deformation based on individual atomic transport, the composition changes which can lead to τcry (c) <texp, hence causing crystallization (blue circles, corresponding to (i) to (iii) in b).
