Controllable introduction of twin boundaries into nanowires

Crystalline nanowires particularly metallic nanowires with twin boundaries have higher strength than those without. Achieving the higher strength requires controllable introduction of twin boundaries, which is impossible at the present. Turning the impossibility to a possibility, this paper proposes a mechanism of controllably introducing twin boundaries into crystalline nanowires by design; and demonstrates its feasibility using molecular dynamics simulations. This mechanism relies on the combination of mechanical torsion and local melting (and subsequent solidification). Under torsion, a nanowire twists by an angle along its axis. Upon local melting, the torsion concentrates at the molten zone. With proper twist angle for each crystal orientation, a geometrically necessary twin boundary forms controllably during solidification of the molten zone. Repeating this process generates controllable patterns of twin boundaries in nanowires. (C) 2010 American Institute of Physics. [doi:10.1063/1.3511366]