Optical effect on the growth of Ni-filled carbon nanotubes using gas/solid interfacial discharge pyrolysis

We report on a growth technique of carbon nanotubes (CNTs) whose core and interlayer spaces were filled with Ni fine particles using discharge pyrolysis at gas/solid interface with optical-parametric-oscillation (OPO) laser beam assist. Transmission electron microscope observation reveals that CNTs were grown at around a cathode spot and, in most cases, Ni fine particles had 3–4 nm diameters. With decreasing the wavelength of OPO laser, G/D ratios obtained from Raman spectrum analysis increased gradually and, in fact, the structures of CNTs were improved from amorphous-like structures to the long and straight CNTs. For longer wavelengths (593 nm, 650 nm) of OPO laser, diameters of CNTs became thicker (typically 10 ~ 100 nm) and therefore, Ni nanowires were formed in the core spaces of CNTs. However, for shorter wavelength (456 nm, 507 nm), diameters of CNTs were significantly reduced and Ni fine particles were embedded in between CNT layers. It was found that the structures of CNTs strongly depend on both...