Selective synthesis and superconductivity of In-Sn intermetallic nanowires sheathed in carbon nanotubes

We demonstrate a simple and reproducible technique to synthesize crystalline and superconducting In-Sn intermetallic nanowires sheathed in carbon nanotubes (CNTs). The method is based on the catalytic reaction of C2H2 over a mixture of both SnO2 and In2O3 particles. Importantly, tetragonal beta-In3Sn and hexagonal gamma-InSn4 nanowires with diameters of less than 100 nm are selectively synthesized at different SnO2 to In2O3 weight ratios. CNTs may serve as cylindrical nanocontainers for continuous growth of liquid-phased In1-xSnx nanowires during growth process as well as for their solidification into In-Sn intermetallic nanowires during the cooling process. Microscopic and spectroscopic analyses clearly reveal evidence of a core-shell structure of the CNT-sheathed In-Sn intermetallic nanowires. Magnetization measurements show that the superconducting In-Sn nanowires have a critical magnetic field higher than the value of their bulk intermetallic compounds. Our method can be adopted to the nanofabrication of analogous binary and ternary alloys.