Thermomechanical Nanomolding of 2D Nanostructures

Fabrication of nanostructures with tight control of chemical composition, morphology, and structure over wafer-scale distances remains a challenge for traditional nanofabrication techniques. Thermomechanical nanomolding (TMNM), a recently developed technique whereby a polycrystalline feedstock is pressed against a mold with 1D pores at elevated temperature and pressure, has been shown to form periodic single crystal, defect free nanowires with high aspect ratios over centimeter length scales (PRL 124, 036102 (2020). Importantly, TMNM is material-agnostic and has been successful with a wide range of materials including metals, alloys, intermetallics, and metal-phosphides.

Here, we extend TMNM to 2D nanostructures. Using 2D Si trenches with a 40 nm width and 500 nm depth as a mold, we fabricate Cu nanostructures using both Cu foil and single crystal Cu as bulk feedstock. S/TEM and SEM imaging confirm successful molding over millimeter distances with aspect ratios > 10; however, the final structures are not always single crystal and possess deformation twins, in contrast to TMNM-fabricated nanowires. We relate the differences in grain and defect structure to different boundary conditions during molding in 1D vs 2D and the role of interfacial energy between the mold and Cu in driving solid-state diffusion.