Synthesis of Ni nanowire-encapsulated carbon nanotubes

A novel method for synthesizing nanowire-encapsulated carbon nanotubes (CNTs) under a high-vacuum ambient is demonstrated. A mixture of acetylene (C₂H₂) and ammoniac (NH₃) gases was effused through a molecular beam (MB)-nozzle onto a small area of a Ni mesh sample heated at 580°C using a newly developed MB-chemical vapor deposition (CVD) system. The densely distributed CNTs, which grew by the thermal decomposition of gases on the intensely gas-effused area, were almost identical in diameter (∼9 nm) despite a large difference in length (0.1-1 μm), and were almost completely filled with a single Ni nanowire of 6 nm in diameter. CNTs with discontinuous filling or those without filling were not observed. On the basis of the detailed transmission electron microscopy (TEM), the base growth mode accompanied by the diffusion of catalyst Ni atoms toward the growth sites was proposed to account for an extremely high rate of filling with nanowire into CNTs.