Thermomechanical Nanomolding in 2D

Fabrication of intermetallic nanostructures over wafer-scale distances is critical for applications such as catalysis, energy storage, and microelectronics. Current top-down and bottom-up fabrication approaches, such as CVD or colloidal synthesis, are limited to simple material compositions, have poor morphology and size variance, and lack control of crystallinity. Recently, thermomechanical nanomolding, whereby a polycrystalline feedstock is pressed through a mold with 1D pores at an elevated temperature (~0.5<i>T_m</i>), has been shown by Jan Schroers’ group at Yale University to form periodic arrays of single crystal, defect free nanowires. Since composition is determined by the feedstock material, this technique can be easily used to form nanowires of a wide range of intermetallic compounds.<br/>Building upon this work, we investigated thermomechanical nanomolding for fabrication of 2D nanostructures. Using 2D Si trenches with a SiO₂ liner as a mold, we successfully nanomold both single element and intermetallic compounds over ~1 cm distances. SEM, EBSD, and S/TEM imaging confirm that 2D linear trenches can be formed with no apparent gaps; however, the final structures are not always single crystal, in contrast to 1D nanomolding. While 1D nanowire growth is driven by interfacial diffusion, the lower surface to volume ratio and post-mold structures indicate that other growth mechanisms, such as deformation twinning and grain reorientation, play an important role during nanomolding.