Multiscale patterning of a metallic glass using sacrificial imprint lithography

Bulk metallic glasses(BMGs)have been developed as a means to achieve durable multiscale,nanotextured surfaces with desirable properties dictated by topography for a multitude of applications.One barrier to this achievement is the lack of a bridging technique between macroscale thermoplastic forming and nanoimprint lithography,which arises from the difficulty and cost of generating controlled nanostructures on complex geometries using conventional top-down approaches.This difficulty is compounded by the necessary destruction of any resulting reentrant structures during rigid demolding.We have developed a generalized method to overcome this limitation by sacrificial template imprinting using zinc oxide(ZnO)nanostructures.It is established that such structures can be grown inexpensively and quickly with tunable morphologies on a wide variety of substrates out of solution,which we exploit to generate the nanoscale portion of the multiscale pattern through this bottom-up approach.In this way,we achieve metallic structures that simultaneously demonstrate features from the macroscale down to the nanoscale,requiring only the top-down fabrication of macro/microstructured molds.Upon detachment of the formed part from the multiscale molds,the ZnO remains embedded in the surface and can be removed by etching in mild conditions to both regenerate the mold and render the surface of the BMGs nanoporous.The ability to pattern metallic surfaces in a single step on length scales from centimeters down to nanometers is a critical step toward fabricating devices with complex shapes that rely on multiscale topography for their intended functions,such as biomedical and electrochemical applications.