Templated one-step catalytic fabrication of uniform diameter Mg_xB_y nanostructurest

摘要

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 nanotubeanowire, 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.