Formation of density controlled Cr-filled carbon nanotubes on Au–Cr solid solution

Abstract

Whisker-like carbon nanotubes with a controlled density (∼8.5×107tubes∕cm2) can be prepared on Au–Cr solid solution films with Cr concentration of 22.5–30.0atomic%, by thermal chemical vapor deposition using Ni-phthalocyanine as precursor. An inner hollow of the nanotube is filled with a single crystalline nanowire composed of Cr atoms. Crystal structure of those nanowires mostly agrees with that of the fcc type Au–Cr solid solution, and rarely takes a metastable structure such as A15 type of Cr as well as oxide (Cr3O4) or carbide (Cr3C2). It is suggested that Ni catalysis does not contribute in the form of nanoparticles to the growth processes of those nanotubes, but in the form of ultra-thin Ni film having many nanoholes. Those films play an important role to dissolve both Cr atoms and C atoms, and offer a stage for active surface diffusion of those atoms precipitated on those films.