Catalyst-assisted growth of single-crystalline hafnium carbide nanotubes by chemical vapor deposition

Single-crystalline hafnium carbide (HfC) nanotubes were synthesized by a one-step catalyst-assisted chemical vapor deposition (CVD) method. The typical nanotubes had uniform diameters of ∼60 nm and wall thicknesses of ∼15 nm and preferentially grew along [201]. From HRTEM/EELS analysis, the growth mechanism based on carbon nanotubes (CNT) tip growth and CNT-templated reaction was proposed for explaining the formation of HfC nanotubes. According to the mechanism, CNTs were first formed by diffusion of C atoms on the surface of solid Ni catalyst particles. Then, gaseous Hf species reacted with C atoms from CNTs to form HfC nanotubes. During the entire growth process, Hf atoms did not participate in the catalytic reaction. Thus, this process was distinguished from the conventional vapor-liquid-solid process.