Controllable nanoshaping of metallic glass through thermoplastic drawing

Metallic nanostructures such as tips, rods, tubes, and wires are important in nanoscale devices and characterization of size-effects in metals. However, these technological and scientific advancements are hampered by the complex and expensive lithography-based fabrication approach. The lack of a cost-effective and scalable nanofabrication venue for metallic material is in direct contrast to the various nanoshaping approaches available for polymeric materials. The origin of this disparity in processing ability is because the polymers exhibit tunable rheological and interfacial properties, which are absent in conventional metals. Unlike conventional metals, amorphous metals (metallic glasses) exhibit supercooled liquid state which mimics rheology of plastics at moderate temperatures. Here we manipulate the supercooled liquid state of metallic glasses to develop a lithography-free nanomanufacturing scheme through elongation and rupture. The metallic glass supercooled liquids confined in a macroscopic cavity and subsequently downsized to nanoscale by stretching. The extent of size-reduction can be controlled by tuning the active volume of liquid and the viscous and capillary stresses. Structures in sub-micron length scales, such as nanowires and nanotips, can be predictably fabricated without using lithography or expensive molds. A systematic study is performed using glass forming Pt-Cu-Ni-P alloy to understand the effects of viscosity, surface tension, pulling velocity, and initial size on the evolution of cylindrical liquid column under tension. The results are quantitatively described by combining the lubrication theory with the capillary induced breakup of liquid filaments. A new manufacturing approach based on variable pulling velocity and/or spinning of metallic liquid is proposed for fabrication of complex geometries. The potential applications of metallic glass geometries fabricated through drawing are discussed.