Templated one-step catalytic fabrication of uniform diameter MgxBy nanostructures

Abstract

Direct fabrication of Mg_xB_y nanostructures is achieved by employing Ni–Mg incorporated MCM-41 in the Hybrid Physical–Chemical Vapor Deposition (HPCVD) reaction. Different reaction conditions are tested to optimize the fabrication process. TEM analysis shows the fabrication of Mg_xB_y nanostructures starting at a reaction temperature of 600 °C, and the yield of the nanostructures increases with the reaction temperature. The as-synthesized Mg_xB_y nanostructures have the diameters in the range of 3–5 nm, which do not increase with the reaction temperature. EELS analysis of the template removed nanostructures confirms the existence of B and Mg with minimal contamination of Si and O. NEXAFS and Raman spectroscopy analyses suggested a concentric layered structure for our as-synthesized Mg_xB_y nanotube/nanowire, which is in good agreement with the theoretical calculations. Ni K-edge XAS indicates that the formation of MgNi alloy particles is important for the Vapor–Liquid–Solid (VLS) growth of Mg_xB_y nanostructures with fine diameters, and the presence of Mg vapor not just Mg in the catalyst is crucial for the formation of Ni–Mg clusters. Physical templating by MCM-41 might also help to confine the diameter of the nanostructures. DC magnetization measurements indicate possible superconductive behaviors in the as-synthesized sample.