Nanomolding Single-Crystalline CoIn₃ and RhIn₃ Nanowires

Intermetallic nanostructures are desirable for catalysis applications and the study of topological materials, owing to the maximization of active catalytic sites as well as the enhanced contributions of topological surface states at the nanoscale, respectively. Fabricating such nanostructures is often challenging, especially for compounds comprised of elements with large differences in melting points, vapor pressures, or diffusivities, due to the complicated reaction pathways and potentially uncontrolled stoichiometries that may entail. To address this challenge, we have employed thermomechanical nanomolding – i.e. hot-pressing of bulk materials into nanoporous molds – to fabricate CoIn₃ and RhIn₃ nanowires with diameters down to ~ 20 nm and lengths exceeding 10 microns. Using scanning transmission electron microscopy (STEM) and STEM electron energy-loss spectroscopy (EELS), we demonstrate the single-crystalline nature of the wires and the diffusion of Co and In from the bulk crystal into the nanopores, thus elucidating the nanowire formation mechanism therein. Temperature-dependent resistivity measurements demonstrate the metallicity of the wires, and their room-temperature resistivities are measured to be 140 and 275 μΩ.cm for CoIn₃ and RhIn₃, respectively, which is about 3-4 times the calculated bulk value in the case of CoIn₃. DFT calculations indicate that Co and In vacancies can shift the Fermi level and introduce substantial scattering that could explain the increased resistivity in CoIn₃ nanowires. Our study demonstrates the scalable synthesis of single-crystalline intermetallic nanowires combining elements with large differences in melting points and vapor pressures (such as Co, Rh versus In). The nanowire diameters and aspect ratios are well-controlled, making them exceptionally suitable for potential applications in catalysis and further studies on the structural and electronic properties at the nanoscale.